UC-NRLF 


HE 


!'    Ml 


LIBRARY 

OF  THE 

UNIVERSITY  OF  CALIFORNIA. 


Class 


PRINCIPLES  OF  HEATING 


A  practical  and  comprehensive  treatise 
on  Applied  Theory  in  Heating* 


By  WILLIAM  G*  SNOW, 

Member 

American  Society  of  Mechanical  Engineers. 
American  Society  of  Heating  and  Ventilating  Engineers. 


NEW  YORK 
DAVID  WILLIAMS  COMPANY 

J4-J6  Park  Place 


'.EHAL1 


Copyright,   1907. 
DAVID  WILLIAMS  COMPANY. 


PRINCIPLES  OF  HEATING. 

PREFACE. 

While  the  title  of  this  book  may  not  be  sufficiently  compre- 
hensive, it  perhaps  expresses,  as  nearly  as  may  be  done  in  a  few 
words,  the  contents  of  the  following  pages.  These  are  largely 
made  up  of  a  collection  of  articles  by  the  author,  which  have  ap- 
peared from  time  to  time  during  the  past  few  years  in  the  Metal 
Worker,  Plumber  and  Steam  Fitter. 

These  contributions  have  been  supplemented  by  reprints  of 
articles  relating  to  heating  prepared  by  other  writers. 

Included  in  this  work  are  the  results  of  tests  made  by  the 
author  on  heating  apparatus  and  systems,  together  with  numer- 
ous original  tables  and  charts  which  he  has  found  to  be  of  prac- 
tical use  in  the  solution  of  heating  problems. 

Considerable  space  is  devoted  to  a  collection  of  articles  on 
Vacuum  and  Vapor  systems  of  heating,  in  view  of  the  amount  of 
interest  manifested  of  late  in  this  class  of  apparatus. 

Special  stress  has  been  laid  on  the  application  of  the  heat  unit 
to  the  solving  of  heating  problems. 

It  is  hoped  that  by  the  aid  of  the  complete  table  of  contents 
and  the  index  persons  interested  in  the  subject  treated  will  find 
the  data  contained  in  the  following  pages  convenient  for  refer- 
ence. 

BOSTON,  1907.  WILLIAM  G.  SNOW. 


161903 


TABLE    OF    CONTENTS. 


CHAPTER    I. 

HEATING     POWER     OF     FUELS,     BOILERS     AND     COMBINATION 

HEATERS. 

The   Heat   Unit 7 

The  Heating  Power  of  Fuels,  etc 8 

Efficiency  of  Boilers  and  Coal  Consumption 8 

Computing  Grate  Surface  on  a  Heat  Unit  Basis 10 

Heating  Surface  in  Boilers  and  Furnaces 10 

Hot  Water  Combination  Heaters 1 1 

Dome  Heater 12 

Ring  Heaters 12 

Vertical  Slab  Sections 13 

Pipe  Coil  Heaters 14 

Types  of  Combination  Heaters 16 

CHAPTER    II. 
GAS,  OIL  AND  ELECTRICITY  vs.  COAL. 

General   Discussion 17 

Electric  Heating 21 

CHAPTER    III. 

THE  CAPACITY  AND  FUEL  CONSUMPTION  OF  HOUSE  HEATING 

BOILERS. 

How  Compute  Size  of  Boiler 23 

Rate  of  Combustion 23 

Amount  of  Fuel  for  a  Season 25 


CHAPTER    IV. 
FURNACE  TESTS. 

Tests  on  the  Rate  of  Combustion  in  Furnaces  and  the  Ve- 
locity of  Air  in  the  Pipes 27 

A  Cold  Day  Test 27 

Data  on  Size  of  Rooms,  Pipes,  and  the  Flow  of  Air 28 

Other   Tests 29 

Advantages  of  Air  Supply  at  Relatively  Low  Tempera- 
tures    30 

CHAPTER    V. 

SPECIFIC  HEAT,  THE  HEATING  AND  COOLING  OF  AIR  AND  HU- 
MIDITY. 

Specific  Heat  and  the  Heating  and  Cooling  of  Air 31 

Cooling    Air 32 

Mechanical  Equivalent  of  Heat 33 

Evaporation  and  Humidity 34 

CHAPTER    VI. 
HEAT  'GIVEN  OFF  BY  DIRECT  RADIATORS  AND  COILS. 

Notes  on  Heat  Emitted  by  Direct  Radiators 37 

Heat  Given  Off  by  Indirect  Radiators 40 

Heat  Given  Off  by  Heaters  Combined  with  Fans 44 

Temperature  of  Air  Required  to  Heat  Rooms  by  Indirect 

Radiation     45 

Size  of  Aspirating  Heaters  or  Coils 48 

CHAPTER    VII. 
THE  Loss  OF  HEAT  BY  TRANSMISSION,  COMPUTING  RADIATION. 

Computation  of  Heat  Losses  and  Radiation 54 

Computing  Direct  Radiation  on  the  Heat  Unit  Basis 56 

The  Boiler  Horse-Power  and  Radiating  Surface  Required 

to  Heat  Isolated  Buildings 63 

Size  of  Heaters  v/ith  Blower  Systems 64 

Relative  Loss  of  Heat  from  Buildings  Having  the  Same 

Cubic    Contents 67 


CHAPTER   VIII. 
HEATING  WATER. 

Heating  Water  by  Submerged  Steam  Pipes. 68 

Hot  WTater  Generators 69 

Boiling  Liquids  in  Vats 7° 

Heating  Small  Swimming  Pools 71 

Heating  Large  Swimming  Pools 73 

Amount  of  Steam  and  Size  Boiler  Required 73 

Amount  of  Steam  Pipe  Required 74 

Size   Boiler  Required 74 

Tank    Heaters 75 

Water  Backs  and  Gas  Heaters 77 

CHAPTER    IX. 

THE  FLOW  OF  STEAM  IN  PIPES  AND  THE  CAPACITIES  OF  PIPES 
FOR  STEAM  HEATING  SYSTEMS  AND  FOR  STEAM  BOILERS. 

A  Comparison  of  Formulas 81 

Application  of  Factors  to  Table  XVI 82 

Resistances  to  the  Flow  of  Steam 83 

Effect   of   Condensation 85 

Steam  Flow  With  More  Than  40  Per  Cent.  Drop  in  Pres- 
sure      86 

Relative  Capacities  of  Pipes 86 

Sizes  of  Steam  Heating  Mains 88 

Sizes  of  Risers — One-Pipe  System 90 

Sizes  of  Risers — Two-Pipe  System 91 

Pipe  Sizes  for  the  Two-Pipe  Vacuum  System  of  Steam 

Heating   92 

Comparison  of  Different  Methods  of  Determining  the  Size 

of  Steam  Mains  to  Supply  Radiating  Surfaces 94 

Low  Pressure  Heating  Mains 99 

Sizes  of  Main  Steam  Pipe  Connections  with  Boilers 102 

Sizes  of  Steam  and  Exhaust  Pipes  for  Engines 103 

Effect  of  Back  Pressure  on.  Simple  Automatic  Engines.  ...  105 

Effect  of  Back  Pressure  on  Compound  Engines 105 

Counteracting  Back  Pressure  by  Increased  Boiler  Pressure  106 

Steam  Heating  in  Connection  with  Condensing  Engines.  .  106 


CHAPTER    X. 
CAPACITIES  OF  PIPES  FOR  HOT  WATER  HEATING. 

The  Flow  of  Water  in  Pipes 108 

Volume  of  Water  to  Supply  Radiators.  .  . 109 

The  Velocity  in  Hot  Water  Heating  Pipes no 

Radiating  Surface  Supplied  by  Pipes  of  Different  Sizes.  .  no 

Pipe  Sizes  for  Indirect  Heating 112 

Sizes   of   Risers 113 

Radiator  Connections 114 

Elbows  and  Bends 115 

Expansion    Tanks 115 

CHAPTER    XI. 

VACUUM  AND  VAPOR  SYSTEMS  OF  STEAM  HEATING. 

The  Webster  System 117 

Heating  at   Night 1 18 

Back  Pressure  Valves  and  Pressure  Reducing  Valves.  ...  119 

Advantages  Claimed 119 

Pipes,    Sizes 122 

The   Paul   System 123 

Absence  of  Back   Pressure 125 

Steam  to  Operate  the  Ejector 125 

Advantages  Claimed ^ 125 

Heating  with  Radiators  at  a  Relatively  Low  Temperature  126 
Donnelly  Positive  Differential  System  of  Exhaust  Steam 

Circulation     127 

The  Thermograde  System  of  Steam  Heating 128 

McGonagle  Vacuum  System  for  Low  Pressure  Plants.  ...  131 

Suggestions  to  Fitters 133 

The  K-M-C  Vacuum  System  (Morgan  Patents) 134 

The  Trane  Vacuum  System 137 

Advantages    Claimed    for    the    Mercury    Seal     Vacuum 

System 139 

Comparison  with  Hot  Water  Heating 141 

Vacuum  Air  Valves  and  the  Norwall  System 141 

Gorton  Vapor  Vacuum  System  of  Heating 143 

Broomell's  Vapor  System  of  Heating 146 

Advantages.  Claimed  for  the  Vapor  System 150 


CHAPTER  I, 


HEATING    POWER   OF    FUELS,  BOILERS   AND  COMBI- 
NATION  HEATERS. 

THE   HEAT   UNIT. 

What  the  pound  is  to  the  grocer,  and  the  2-foot  rule  is  to  the 
carpenter,  the  heat  unit  should  be  to  those  engaged  in  heating  and 
ventilating  work.  It  is  their  unit  of  measurement  and  is  the  com- 
mon sense  basis  of  all  heating  calculations.  Briefly  stated,  a  heat 
unit  is  the  amount  of  heat  required  to  raise  the  temperature  of  I 
pound  of  water  i  degree  F. 

To  make  practical  use  of  the  heat  unit  one  must  become  famil- 
iar with  the  heating  power  of  fuels,  the  loss  of  heat  through  walls 


THE   METAL   WORKER 

Fig.   1. — Horizontal   Tubular  Boiler. 

and  glass,  the  heat  emitted  by  radiators  and  many  other  facts  bear- 
ing on  the  subject.  It  is  hoped  this  information  will  prove  useful 
to  those  who  wish  to  know  the  "  whys  and  wherefores  "  of  heat- 
ing calculations  and  are,  not  content  to  blindly  follow  "  thumb 
rules,"  which  may  be  good  enough  for  small  work,  but  for  large 
undertakings  are  apt  to  give  very  unsatisfactory  results  and  bring 
a  serious  loss  to  the  contractor.  A  good  grasp  of  the  "  heat  unit 
basis  "  gives  one  confidence  to  attack  and  the  ability  to  solve  al- 
most any  heating  problem  that  may  arise. 

7 


8  Principles   of   Heating. 

THE    HEATING    POWER    OF    FUELS,    ETC. 

Anthracite  coal  has  a  theoretical  heating  power  of  about  14,200 
heat  units  per  pound  of  combustible.  With  10  per  cent,  ash  and 
noncombustible  matter,  I  pound  has  a  heating  power  of  about 
13,000  heat  units.  The  smaller  the  coal  the  greater  the  percentage 
of  ash,  16  per  cent,  or  more  being  not  uncommon  with  the  smaller 
sizes. 

Coke,  like  anthracite  coal,  consists  almost  entirely  of  carbon 
and  has  about  the  same  heating  power. 

Good  bituminous  coal  has  a  heating  power  of  about  13,000  to 
14,000  heat  units  per  pound  of  combustible. 

About  2^/2  pounds  of  dry  wood  have  the  same  heating  power 
as  a  pound  of  coal. 

Taking  a  fair  average,  25,000  cubic  feet  of  natural  gas,  or 
40,000  cubic  feet  of  illuminating  gas,  are  equivalent  in  heating 
power  to  a  ton  of  coal.  A  cubic  foot  of  ordinary  illuminating  gas 
has  a  heating  power  ranging,  as  a  rule,  from  600  to  700  heat 
units. 

The  heating  power  of  I  pound  of  crude  petroleum  is  about 
21,000  heat  units,  the  refined  oil,  or  kerosene,  having  a  heating 
power,  in  round  numbers,  of  27,000  to  28,000  heat  units. 

Electrical  heat  units  are:  I  kilowatt  hour  equals  3412  heat 
units;  I  watt  hour  equals  3.412  heat  units;  I  heat  unit  equate 
0.293  watt  hours. 

A  person  gives  off  about  400  heat  units  per  hour,  an  ordinary 
gas  burner  approximately  4,000  heat  units  and  an  incandescent 
electric  light  of  16  candle-power  about  190  heat  units. 

EFFICIENCY  OF  BOILERS  AND   COAL  CONSUMPTION. 

To  determine  the  probable  coal  consumption  in  a  heating  boiler 
one  must  assume  a  certain  efficiency.  It  is  of  interest  in  this  con- 
nection to  discuss  briefly  the  efficiency  and  coal  consumption  of 
high  pressure  boilers  of  the  types  shown  in  Figs,  i  and  2,  and  to 
show  the  application  of  the  heat  unit  in  solving  problems  of 
this  nature.  A  boiler  horse-power  is  equivalent  to  33,305  heat 
units  per  hour;  hence  3  pounds  of  combustible  per  horse-power 
is  equivalent  to  11,102  heat  units  out  of  a  possible  14,000  in 
round  numbers,  representing  an  efficiency  of  about  80  per  cent. 
With  4  pounds  of  combustible  per  horse-power  these  figures 


Heating   Power   of   Fuels.  9 

would  be  reduced  to  8,326  and  60  per  cent,  respectively,  the  latter 
conforming  more  nearly  to  ordinary  working"  conditions  than 
does  80  per  cent.  Suppose  a  boiler  evaporates  9  pounds  of  water 
per  pound  of  coal  containing  about  16  per  cent,  ash ;  then  I  pound 
of  coal  will  contain  only  about  5/c  pound  of  combustible,  or  the 
evaporation  will  be  equivalent  to  about  u  pounds  of  water  per 
pound  of  combustible.  To  evaporate  I  pound  of  water  at  a  tem- 
perature of  212  degrees  F.  into  steam  at  the  same  temperature 
requires  about  964  heat  units ;  hence  the  evaporation  of  1 1  pounds 


Fig.  2. — Water  Tube  Boiler. 


of  water  by  I  pound  of  combustible  is  equal  to  10,604  heat  units 
per  pound,  or  approximately  76  per  cent,  of  the  theoretical  amount 
of  heat  in  the  coal. 

Such  an  efficiency  may  be  obtained  under  well  managed  high 
pressure  boilers,  but  smaller  cast  iron  heating  boilers,  illustrated 
in  Figs.  3  and  4,  will  with  the  less  skillful  attendance  given  them 
have  hardly  more  than  60  per  cent,  efficiency.  In  other  words, 
we  would  not  be  likely  to  transfer  from  the  fire  to  the  water  in 
the  heater  more  than  8,000  to  9,000  heat  units  per  pound  of  coal. 

The  distinction  between  coal  and  combustible  must  be  kept  in 
mind,  the  latter  being  only  the  burnable  portion  of  the  fuel. 


10 


Principles    of   Heating. 


COMPUTING  GRATE  SURFACE  ON  A  HEAT  UNIT  BASIS. 

A  knowledge  of  the  heat  utilized  per  pound  of  coal  burned  and 
the  total  loss  of  heat  from  a  building,  the  latter  to  be  computed 
as  described  later,  gives  a  convenient  basis  for  determining  the 
size  of  the  heater,  irrespective  of  the  total  radiating  surface,  on 
which  the  size  is  commonly  based.  If  each  pound  of  coal  burned 
gives  up  to  the  water  in  the  heater  8,000  heat  units ;  dividing  the 
total  heat  loss  per  hour  from  the  building  by  8,000  gives  the 
weight  of  coal  that  must  be  burned.  The  grate  surface  is  then 


THE. METAL  WOKKlt 


Fig.  3. — Sectional  Cast  Iron  Boiler  with  Vertical  Sections. 

determined  by  dividing  the  weight  just  computed  by  3  to  4  for 
small  boilers,  4  to  5  for  those  of  medium  size,  and  by  5  to  7  for 
large  sized  boilers.  These  figures  represent  permissible  rates  of 
combustion,  expressed  in  pounds  of  coal  burned  per  square  foot 
per  hour  in  house  heaters. 

HEATING  SURFACE  IN  BOILERS   AND  FURNACES. 

The  proper  grate  surface  is  only  one  element  to  be  determined. 
It  is  equally  important  to  see  that  the  heater  selected  has  the 
proper  amount  of  heating  surface  well  located.  As  to  the  amount 
of  heat  absorbed  per  square  foot  of  heating-  surface,  the  small 


Heating    Power    of    Fuels. 


1 1 


boilers  mentioned  commonly  have  only  10  to  15  square  feet  of  heat- 
ing surface  per  square  foot  of  grate,  the  medium  sizes  16  to  20, 
and  the  larger  ones  20  to  25.  These  proportions,  with  the  rates 
of  combustion  stated,  give  from  2,000  to  2,200  heat  units  absorbed 
per  hour  per  square  foot  of  heating  surface. 

Hot  air  furnaces  commonly  have  15  to  20  square  feet  of  heat- 
ing surface  to  each  square  foot  of  grate.  Taking  the  average, 
17^2,  and  a  5-pound  rate  of  combustion,  the  heat  emitted  per 


square    foot    of    heating    surface    would    be 


C      V     g    QQQ 

-  -  -  '  —  — 


=  2,400. 


This  figure  is,  of  course,  only  approximate,  the  kind  and  location 


THE   METAL   WORKS" 

Fig.  4. — Sectional  Cast  Iron  Boiler  with  Horizontal  Sections. 

of  the  heating  surface  making  some  portions  more  effective  and 
others  less  so  than  the  average.  The  heat  given  off  varies  also 
with  the  rate  of  combustion,  but  not  at  all  in  proportion  to  it. 

HOT  WATER  COMBINATION    HEATERS. 

At  best  it  is  difficult,  in  a  combination  system  of  heating,  to 
secure  a  proper  balance  between  the  hot  water  and  hot  air.  Much 
depends  on  the  proper  rating  of  the  coil  or  special  casting  used 
for  heating  the  water.  A  number  of  tests  made  by  the  writer  on 
various  types  of  these  heaters  have  established  ratings  which  may 
safely  be  used  in  proportioning  systems  of  this  kind.  In  making 
the  tests,  radiators  were  arranged  so  that  the  total  amount  of  sur- 
face connected  with  the  heater  could  be  nicely  regulated  to  de- 


12 


Principles    of   Heating. 


termine  the  total  radiating  surface  that  could  be  maintained  at  an 
average  temperature  of  about  160  degrees  for  hours  at  a  time 
with  an  even  fire  and  an  ordinary  rate  of  combustion. 

DOME   HEATER. 

A  dome  shaped  cast  iron  section,  of  the  general  type  illustrated 
in  Fig.  5,  proved  capable  of  maintaining  an  average  temperature 
in  the  flow  pipe  of  about  160  degrees  when  supplying  approxi- 
mately 15  square  feet  of  radiating  surface  to  each  square  foot  of 
heating  surface.  A  great  increase  in  capacity  was  noted  when 
the  fire  was  bright  on  top,  the  heater  then  being  subjected  to  the 
direct  rays  from  the  burning  coal.  At  other  times  it  was  merely 


Til!]]  IN — 
||[|  ||4 


"DEEP! 


DOME  WATER  HEATER 
Fig.  5? — Type  A. 


RING  WATER  HEATER 

Fig.  6. — Type  B. 


surrounded  by  hot  gases.    The  rating  given  is  that  under  average 
conditions  during  an  eight-hour  run. 

RING  HEATERS. 

A  fire  pot  having  a  cored  space  4^2  inches  high  by  about  I 
inch  wide  extending  around  the  entire  circumference,  as  shown 
in  Fig.  6,  was  next  tested.  Three  tests,  each  of  about  eight  hours' 
duration,  showed  this  type  of  combination  heater,  having  a  total 
of  5  square  feet  of  heating  surface,  to  be  capable  of  heating  to 
an  average  temperature  of  170  degrees,  the  water  in  the  flow  pipe 
connected  with  250  square  feet  of  direct  radiation.  This  is  equiva- 
lent to  a  capacity  of  50  square  feet  of  direct  radiation  to  every 
square  foot  of  heating  surface  in  contact  with  the  fire.  A  combi- 
nation of  the  ring  and  the  dome  shown  in  Fig.  7,  has  the  heating 
capacity  stated  in  Table  I. 

Another  combination  heater  of  a  similar  type,  shown  in  Fig.  8. 


Heating   Power   of   Fuels.  13 

was  tested,  the  cored  portion  of  the  fire  pot  being  8  inches  high, 
or  about  two-thirds  the  depth  of  the  fire.  Three  eight-hour  tests 
proved  these  heaters  capable  of  heating  the  water  in  the  flow  pipe 
to  about  1 60  degrees  when  connected  with  approximately  300 
square  feet  of  radiation.  This  heater  had  nearly  twice  the  surface 
of  the  one  previously  described,  yet  the  radiating  surface  carried 
was  only  about  20  per  cent,  more  and  was  not  so  hot.  Only  about 
30  square  feet  of  radiating  surface  was  supplied  per  square  foot  of 
heating  surface  exposed  to  the  fire.  The  rapid  falling  off  in  ef- 
ficiency was  due  to  the  chilling  effect  on  the  fire  of  so  large  a  body 
of  water,  necessitating  more  frequent  attention  than  with  the 


COMBINED  RING 
AND  DOME  HEATER 

Fig.  7.— Typo  C.— A  Combination  of  A  and  B. 


DEEP  RING 
WATER  HEATER 

Fig.  8. — Deep  Form  of  Type  B. 


other  combination  heaters  tested.  The  average  rate  of  combustion 
during  the  tests  was  about  3^2  pounds  of  hard  coal  per  square 
foot  of  grate  surface  per  hour. 

In  each  of  the  three  series  of  tests  the  drop  in  temperature 
between  the  flow  and  return  pipes  was,  on  an  average,  about  20 
degrees  and  remained  nearly  uniform  throughout. 

VERTICAL  SLAB  SECTIONS. 

Some  makers  who  use  vertical  hollow  cast  iron  slabs  in  con- 
nection with  brick  lined  furnaces  rate  them  as  high  as  75  square 
feet  of  radiating  surface  per  square  foot  of  heating  surface.  This 
rating  is  50  per  cent,  greater  than  the  highest  one  stated 
above.  With  a  brisk  fire  there  is  no  question  that  a  square  foot 


14  Principles    of    Heating. 

of  heating  surface  in  direct  contact  with  the  fire  will  carry  at  least 
75  square  feet  of  heating  surface,  but  it  seems  hardly  wise  to 


PIPE  COIL 
WATER   HEATER 

Fig.  9. — Type  F. 


reckon  on  its  doing  so  right  along,  in  view  of  the  kind  of  attention 
commonly  bestowed  on  furnace  fires. 


PIPE    COIL    HEATERS. 


Coils  of  ij4  or  i  YZ -inch  pipes,  as  shown  in  Fig.  9,  make  an  ex- 
cellent form  of  heater  to  combine  with  furnaces,  especially  if  ar- 
ranged so  that  the  lower  portion  may  be  either  above  the  fire  or 
buried  in  it,  according  to  the  hight  at  which  the  fire  is  carried, 


Fig.  10. — Auxiliary  Heater  for  Combination  Heating. 

thus  giving  a  ready  means  of  regulating  the  temperature  of  the 
water ;  since  the  coil,  when  in  contact  with  the  fire,  is  about  twice 


Heating    Power    of    Fuels. 


as  effective  as  when  the  fire  is  kept  several  inches  below  it.  Pipe 
coils,  when  suspended  above  the  fire,  may  -be  rated  to  carry  from 
20  to  25  square  feet  of  radiating  surface  per  square  foot  of  heat- 


Fig.  11. — Types  of  Dome  Heater  for  Combination  Heating. 


Fig.  12. — Disk  Heater  for  Com- 
bination Heating. 


Fig.  13. — Overhanging  Type  of  Auxiliary 
Heater. 


ing  surface,  and  say,  30  to  40  square  feet  when  arranged  as  de- 
scribed, the  lower  strand  of  the  coil  to  be  in  contact  with  the  fire. 
Single  coils  placed  in  the  fire  will  carry  at  least  50  square  feet  of 
surface  per  square  foot  of  coil. 

Work  installed  on  the  basis  of  the  figures  above  given  has 


1 6  Principles    of    Heating. 

proved  satisfactory  under  the  practical  working  conditions  found 
in  dwellings : 

TABLE   I. 

SUMMARY,  GIVING  RATINGS  FOR  DIFFERENT  CLASSES  OF  COMBINATION   HEATERS. 

Rating  expressed  in  the  number 
of  square  feet  of  direct  radia- 
ting surface,  which  may  be 
kept  at  a  temperature  of  160 
degrees  per  square  foot  of 
heating  surface  in  the  corn- 
Description,  bination  heater. 

A. — Cast  iron  sections  suspended  above  the  fire 15  to  20 

B. — *Cast  iron  sections  in  contact  with  the  fire 40  to  60 

C. — A  and  B  combined 25  to  35 

D. — Pipe  coil  suspended  above  the  tire 20  to  25 

E. — Pipe  coil  buried  in  the  fire 50  to  60 

F. — D   and  E   combined 30  to  40 


*  Capacity  decreases  as  the  depth  of  the  surface  in  contact  with  the  fire  is 
increased,  since  the  deeper  the  section  the  greater  the  chilling  effect  of  the 
water  on  the  fire  and  the  harder  to  keep  up  the  latter. 

TYPES   OF   COMBINATION    HEATERS. 

A  number  of  common  types  of  combination  heaters  on  the 
market  are  shown  in  Figs.  10,  n,  12,  13  and  14. 


Fig.  14. — Maltese  Type  of  Auxiliary  Heater. 


CHAPTER  II. 

GAS,  OIL  AND  ELECTRICITY  vs.  COAL. 

The  question  sometimes  comes  up  whether  to  use  gas  or  oil, 
instead  of  coal,  for  heating  purposes.  On  a  heat  unit  basis,  we 
may  not  expect  to  utilize  more  than  8,000  to  9,000  units  from  each 
pound  of  coal  burned.  Comparing  this  with  gas  having  a  heating 
power  of  about  700  heat  units  per  cubic  foot,  and  assuming  that 
75  per  cent,  of  the  heat  is  transferred  to  the  water  in  the  heater, 
we  have  525  heat  units  utilized  per  cubic  foot  of  gas  burned. 
From  a  ton  of  coal  there  would  be  utilized  2,000  (Ibs.)  X 
8,500  (heat  units,  as  a  maximum)  =  17,000,000  heat  units.  This 
amount  divided  by  525  gives  32,400  cubic  feet,  or  the  equivalent 
amount  of  gas  in  heating  effect.  This  volume  of  gas,  at  $i  per 
1,000,  would  cost  more  than  five  times  as  much  as  a  ton  of 
coal  at  $6  per  ton  having  the  same  heating  power.  Of  course, 
the  great  advantages  possessed  by  gas  over  coal  are  the  absence 
of  dirt  and  the  ability  to  instantly  turn  on  or  shut  off  the  heat. 

The  following  statement  by  B.  T.  Galloway,*  who  made  a 
number  of  experiments  on  oil  and  gas  heating,  is  of  interest : 

"  Oil  (and  by  this  material  we  mean  the  refined  product,  kero- 
sene) may  be  dismissed  with  a  few  words,  as,  after  many  trials 
with  numerous  devices,  it  is  found  to  be  impracticable  as  a  means 
of  heating  water  or  generating  steam.  In  all  of  our  experiments 
oil  and  gas  were  used  to  heat  water  circulating  either  in  pipes  or 
ordinary  radiators.  Taking  an  ordinary  heating  plant,  say  with 
a  radiating  capacity  of  500  to  1,000  square  feet,  oil,  when  burned 
in  the  boiler  with  any  of  the  so-called  hydrocarbon  burners,  would 
be  beyond  the  means  of  the  ordinary  house  owner.  The  cost  of 
heating  500  square  feet  of  radiation,  using  kerosene  oil  and  the 
best  devices  we  have  been  able  to  secure  or  make,  would  be  about 
three  times  as  great  for  oil  as  compared  with  anthracite  coal, 
provided  coal  was  selling  at  $6  per  ton  delivered  in  the  cellar,  and 
oil  at  10  cents  per  gallon  delivered  in  the  same  way.  Then  the 

*  See  "Heating  Experiment?  with  Oils  and  Manufactured  Gas,"  by  B.  T.  Gal- 
loway, in  The  Metal  Worker,  Plumber  and  Steam  Fitter,  October  17,  1903. 

17 


i8 


Principles    of    Heating. 


labor  of  handling  oil,  watching  the  burners  and  keeping  the  ap- 
paratus in  order  is  fully  as  great  as  that  connected  with  putting 
on  coal  and  taking  out  ashes.  Furthermore,  we  have  never  seen 
an  oil  device  that  could  be  entirely  trusted,  as  experience  with 
them  shows  that,  when  least  expecting  it,  they  go  wrong,  and  fire 
and  explosion  follow  unless  great  care  is  observed.  The  utiliza- 
tion of  oil,  therefore,  as  described,  is  hardly  to  be  recommended. 

"  There  is  one  method  of  utilizing  oil,  however,  which  is 
worthy  of  further  trial  and  consideration — viz.,  that  of  adopting 
as  a  burner  the  ordinary  blue  flame  oil  stove,  of  which  there  are 


Fig.  15. — Type  of  Electric  Radiator. 

several  kinds  on  the  market.  The  burners  for  these  stoves  can  be 
bought  separately.  They  have  a  gravity  feed,  and  will  run  indefi- 
nitely with  little  care  and  attention. 

"  It  was  found  that  boilers  made  for  coal  with  their  arrange- 
ments for  cinders,  drafts,  etc.,  were  poorly  adapted  for  the  use  of 
a  fuel  as  costly  as  gas.  Only  a  small  portion  of  the  efficient  heat 
units  in  the  gas  could  be  utilized,  the  rest  going  up  the  chimney 
or  being  lost  in  overcoming  the  resistance  offered  by  the  iron  and 
in  other  ways.  With  specially  constructed  boilers,  and  by  such 
we  mean  those  where  the  flame  of  the  burning  gas  can  be  brought 
into  direct  contact  with  a  large  surface  of  some  metal  like  copper, 
much  more  effective  results  can  be  obtained  than  where  ordinary 
boilers  made  for  coal  are  used.  Types  of  such  boilers  are  to  be 
found  in  those  used  for  automobiles  containing  either  a  large  num- 
ber of  small  copper  tubes  or  consisting  of  series  upon  series  of 


Gas,    Oil    and    Electricity    vs.    Coal.  19 

copper  coils  through  wrhich  the  circulating  water  passes.  Even 
with  such  devices,  however,  it  has  been  found  impracticable  to 
sufficiently  heat  the  water  from  a  central  plant,  except  at  a  cost 
considerably  more  than  that  of  coal  at  ordinary  prices.  In  actual 
practice  the  cost  of  the  gas  would  be  about  double  that  of  coal, 
the  price  of  the  latter  being  estimated  at  $6  per  ton,  and  the  for- 
mer at  $i  per  1,000  cubic  feet,  22  candle-power.  Of  course,  in 
this  case  there  is  no  coalman  to  bother  with,  no  ashes  to  take  out 
and  no  trouble  in  regulating  the  apparatus  with  the  proper  de- 


Fig.  ISA. — Luminous  Electric  Radiator. 

vices  at  hand.  Theoretically,  and  practically  too  for  that  matter, 
there  is  no  reason  why  a  householder  could  not  light  his  burner 
in  the  autumn  and  the  apparatus  would  do  the  rest,  until  it  was 
time  to  turn  the  gas  off  in  the  spring.  By  means  of  properly  ad- 
justed regulators,  the  gas  would  be  fed  to  the  burner  in  sufficient 
amounts  to  maintain  a  uniform  temperature  in  the  room  above. 
With  gas  at  present  prices  this  method  of  heating  would  be  prac- 
tically prohibitive  for  many,  notwithstanding  its  advantages." 

Extracts  from  an  article  by  Donald  McDonald  on  "  Domestic 
Heating  by  Gas  "*  seem  worth  repeating  here : 

*  See  "  Domestic  Heating  by  Gas,"  Donald  McDonald,  in  The  Metal  Worker, 
Plumber  and  Steam  Fitter.  October  24,  1903. 


2O  Principles    of   Heating. 

"  Where  the  gas  is  the  only  source  of  heat  and  the  room  is 
occupied  as  a  bed  chamber  it  is  much  better,  although  somewhat 
more  expensive,  to  use  a  closed  heater  provided  with  a  good  flue. 
Such  a  heater  must,  however,  meet  many  very  rigid  conditions ; 
otherwise  the  flue  connection  will  be  worse  than  useless.  First  of 
all,  the  flue  must  be  so  open  and  must  run  so  high  that  a  down 
draft  through  it  will  be  an  impossibility.  A  few  seconds  of  down 
draft,  carrying  with  it  a  load  of  carbonic  acid  and  nitrogen,  will 
put  out  the  fire,  and  the  flue  becoming  cold,  the  down  draft  will 
continue  and  the  apartment  become  full  of  gas.  No  flue  at  all  is 


Fig.  15B. — Non-Luminous  Electric  Radiator. 

much  better  than  this.  The  stove  must  also  be  so  constructed  that 
no  more  air  is  drawn  through  it  than  is  necessary  to  burn  the  gas, 
otherwise  there  will  be  a  great  waste  of  heat  up  the  chimney. 

"  The  amount  of  air  required  to  burn  the  gas,  if  it  is  cooled  to 
300  degrees  before  it  reaches  the  chimney,  will  only  carry  away 
with  it  about  5  per  cent,  of  the  heat.  Closed  stoves,  however,  as 
generally  constructed,  send  up  the  chimney  anywhere  from  20  to 
80  per  cent,  of  the  heat  produced  by  the  gas.  Any  device  which 
sends  a  part  of  the  products  of  combustion  up  the  chimney  and 
the  rest  of  it  into  the  room  is  simply  folly.  The  part  which  reach- 
es the  chimney  is  no  better  and  no  worse  than  the  part  which  is 


Gas,    Oil   and   Electricity    vs.    Coal.  21 

put  into  the  room,  and  unless  care  is  taken  to  send  all  the  products 
of  combustion  up  the  chimney  it  is  much  more  sensible  not  to 
send  any  of  them. 

"  I  have  seen  and  heard  many  learned  discussions  as  to  the 
question  of  whether  a  luminous  flame  or  a  blue  flame  produces 
the  most  heat.  Nearly  all  salesmen  and  dealers  of  gas  stoves  will 
insist  that  the  particular  burner  which  they  are  advocating  pro- 
duces a  great  deal  more  heat  than  any  other  burner.  Of  course, 
any  chemist  or  any  engineer  knows  that  if  the  combustion  is  com- 
plete and  all  the  products  of  combustion  escape  into  the  room  to  be 
heated,  the  room  receives  all  the  heat  due  to  the  combustion  of  the 
fuel,  and  no  amount  of  ingenuity  can  increase  this  I  per  cent.  If 
the  combustion  is  not  complete  the  odor  will  be  so  vile  that  no 
one  will  tolerate  it.  In  other  words,  in  this  class  of  stoves  the 
efficiency  is  almost  always  100  per  cent.,  and  need  not  be  con- 
sidered at  all  in  selecting  them." 

ELECTRIC   HEATING. 

To  determine,  on  the  heat  unit  basis,  what  it  would  cost  to  heat 
a  room  with  electricity  by  means  of  an  electric  radiator,  or  heater, 
as  shown  in  Fig.  15,  let  us  suppose,  for  example,  that  it  is  desired 
to  know  the  cost  of  heating  a  corner  room,  14  x  14  x  10  feet,  ten 
hours  per  day  under  average  weather  conditions.  With,  say,  20 
per  cent,  glass  surface,  the  equivalent  glass  surface,  corresponding 
to  the  exposure,  would  be  (20  per  cent,  of  280  square  feet  =  56 
square  feet)  +  [%  X  (280  —  56)  =56  square  feet]  =  a  total 
of  112  square  feet  of  glass ;  wall  surface  being  rated  as  one-fourth 
as  much  glass  surface.  One  hundred  and  twelve  square  feet 
of  glass  X  85  heat  units  per  square  foot  an  hour  for  70  de- 
grees difference  in  temperature  X  1.25  (the  factor  for  northwest 
exposure)  —  approximately  11,900  heat  units  per  hour.* 

A  certain  allowance  must  be  added  for  quickly  warming  the 
contents  of  the  room,  apart  from  the  transmission  loss  above  com- 
puted. To  do  this  it  is  convenient  to  add  to  the  computed  loss  of 
heat  through  walls  and  windows  a  number  of  heat  units  equal  to 
at  least  one-third  the  cubic  contents;  in  this  case  1-3  X  1,960  = 
653  heat  units.  This  combined  with  the  11,900  heat  units  pre- 
viously  computed,  gives  a  total  of  12,553  neat  units  per  hour. 

¥  See  page  53  and  following  for  a  fuller  discussion   of  computation  of  heat 
losses. 


22  Principles    of   Heating. 

Electric  current,  when  metered,  is  charged  for  on  the  basis  of 
watt  hours,  a  heat  unit  being  equivalent  to  0.293  watt  hour. 
Therefore,  12,553  heat  units  would  be  equivalent  to  3,680  watt 
hours ;  or,  to  heat  the  room  ten  hours  in  zero  weather  by  electricity 
would  require  36,800  watt  hours. 

The  average  amount,  during  the  heating  season,  would  proba- 
bly not  exceed,  for  a  ten-hour  day, -^—  X  36,800  =  15,800  watt 

hours,  approximately.  Ten  cents  per  1,000  watt  hours  is  a  not 
uncommon  rate  for  such  service ;  and  at  this  price  the  cost  to  heat 
the  room  ten  hours  per  day  in  average  weather  would  be  $1.58,  a 
prohibitive  cost. 

With  coal,  such  a  room,  with  a  50  square  foot  steam  radiator, 
would,  in  zero  weather,  allowing  250  heat  units  per  square  foot  of 
radiating  surface  per  hour  and  8,000  heat  units  per  pound  of  coal, 
take  only  50  (square  feet)  X  250  (heat  units)  X  10  (hours)  -r- 
8,000  =  15.6  pounds  of  coal,  costing,  say,  5  cents. 

Electric  heating  is  bound  to  be  expensive  in  comparison  with 
steam,  if  the  exhaust  from  the  power  plant  goes  to  waste,  since 
about  90  per  cent,  of  the  heat  of  the  steam  passes  away  with  the 
exhaust  from  the  engines.  With,  say,  75  per  cent,  boiler  efficiency, 
10  per  cent,  engine  efficiency  on  a  heat  unit  basis  and  85  per  cent, 
on  a  mechanical  basis  (that  is,  allowing  15  per  cent,  for  friction) 
and  90  per  cent,  dynamo  efficiency  and  95  per  cent,  line  efficiency, 
we  have  for  the  combined  efficiency  of  boiler,  engine,  dynamo  and 
wires:  0.75  X  o.io  X  0.85  X  0.90  X  0.95  =  5.45  per  cent.  The 
efficiency  of  a  direct  steam  heating  system  would  probably  be  as 
high  as  55  to  60  per  cent.,  or,  say,  10  times  that  of  the  electric 
heating  system. 


CHAPTER  III. 

THE  CAPACITY  AND    FUEL    CONSUMPTION  OF  HOUSE 
HEATING  BOILERS. 

Manufacturers'  boiler  ratings  vary  so  widely  that  it  is  worth 
while  for  contractors  to  compute  the  capacities  themselves  and 
not  trust  implicitly  the  figures  given  in  the  catalogues.  The  basis 
of  computation  should  be  the  grate  surface  and  the  rate  of  com- 
bustion. In  house  heating  boilers  of  medium  size  not  more  than 
5  pounds  of  coal  should  be  burned  per  square  foot  of  grate  surface 
per  hour.  As  to  a  5-pound  rate  being  a  fair  maximum  to  assume, 
it  may  be  compared  with  horizontal  tubular  boiler  practice  in 
which,  with  easy  firing,  a  10  to  12  pound  rate  is  common.  Such 
boilers  have  33  to  40  square  feet  of  heating  surface  per  square  foot 
of  grate,  whereas  common  sizes  of  house  heating  boilers  have, 
roughly  speaking,  16  to  20.  Hence,  with  half  the  heating  surface 
the  rate  oi  combustion  should  be  proportionally  lower  in  order 
that  the  heat  may  be  as  well  absorbed.  This  would  give  a  5  or  6 
pound  rate  for  house  heaters. 

HOW    COMPUTE   SIZE   OF   BOILER. 

To  ascertain  the  size  of  boiler  necessary  to  supply  a  given 
amount  of  direct  radiation,  say,  1,500  square  feet,  for  example, 
including  the  surface  in  mains,  first  multiply  the  total  surface  by 
the  heat  given  off  per  square  foot  per  hour.  With  hot  water,  in 
the  case  taken  for  illustration,  this  would  be  1,500  X  150  =  225,- 
ooo  heat  units.  Assuming  8,000  heat  units  to  be  utilized  per  pound 
of  coal  burned,  each  square  foot  of  grate,  with  a  5  pound  rate  of 
combustion,  will  give  to  the  water  in  the  boiler  40,000  heat  units 
per  hour.  Therefore  the  grate  surface  required  will  be  225,000  -f- 
40,000  =  5.62  square  feet. 

RATE  OF  COMBUSTION. 

The  rate  of  combustion  should  not  exceed  5  pounds  for  boilers 
having,  say,  not  over  6  or  8  square  feet  of  grate  surface. 

23 


24  Principles    of   Heating. 

Boilers  with  two  or  three  times  as  large  a  grate  are  generally 
cared  for  by  a  paid  attendant,  in  which  case  there  is  no  objection 
to  burning  coal  at  a  faster  rate.  Such  boilers  generally  have  more 
heating  surface  in  proportion  to  the  grate  than  the  smaller  ones, 
hence  the  increased  output  of  heat  will  be  readily  absorbed  and 
the  boiler  will  be  just  as  economical  as  a  smaller  one  burning  coal 
more  slow!}'. 

Small  boilers  with  10  to  15  square  feet  of  heating  surface  per 
square  foot  of  grate  should  be  rated  to  do  their  work  on  a  3  to  4 
pound  rate  of  combustion,  corresponding  to  about  160  to  210 
square  feet  of  hot  water  radiating  surface  per  square  foot  of  grate. 

Medium  size  boilers,  with  16  to  20  square  feet  of  heating  sur- 
face to  I  of  grate,  should  be  based  on  burning  4  to  5  pounds  of 
coal  on  each  square  foot  of  grate  per  hour,  corresponding,  in 
round  numbers,  to  210  to  260  square  feet  of  hot  water  radiation 
per  square  foot  of  grate. 

Large  size  boilers  with  21  to  25  or  more  square  feet  of  heating 
surface  per  square  foot  of  grate  may  be  rated  on  a  coal  consump- 
tion of  6  to  7  pounds  per  square  foot  per  hour,  or  even  a  trifle 
higher  rate,  where  the  heating  surface  is  ample,  corresponding 
approximately  to  320  to  370  square  feet  of  hot  water  radiation 
per  square  foot  of  grate.  With  steam  radiation  giving  off,  say, 
250  heat  units  per  square  foot  per  hour,  the  same  grate  would 
carry  only  150-250  =  3-5  as  much  surface  as  with  hot  water  radi- 
ation. 

The  maximum  night  rate,  when  a  boiler  is  expected  to  run 
at  least  eight  hours  without  attention,  should  not  exceed  4 
pounds,  equal  to  32  pounds  of  coal  burned  on  each  square  foot  of 
grate  in  that  length  of  time.  With  the  4-pound  rate  of  com- 
bustion assumed,  a  fire  one  foot  thick  would  burn  about  half 
through  during  the  night,  leaving  an  ample  quantity  of  uncon- 
sumed  fuel  on  the  grate  to  readily  ignite  the  fresh  fuel  added 
in  the  morning.  With  a  higher  rate  of  combustion  a  thicker  fire 
would  be  necessary.  Too  great  a  depth,  however,  would  inter- 
fere with  the  draft. 

One  of  the  essentials  in  a  house  heating  boiler  is  a  fire  box 
of  sufficient  depth  to  permit  carrying  a  good  deep  fire.  Thin  fires 
require  too  frequent  attention.  Avoid  boilers  with  grates  of  ex- 


f 


Fuel    Consumption.  25 


cessive  length,  owing  to  the  difficulty  of  properly  handling  the 
fire. 

AMOUNT  OF  FUEL  FOR  A  SEASON. 

To  compute  the  season's  coal  consumption  in  a  house  is,  as 
heating  men  know,  a  very  uncertain  problem.  The  radiating  sur- 
face or  the  grate  area  may  be  taken  as  a  basis.  If  the  boiler  is 
properly  proportioned  for  its  work,  so  that  the  maximum  rate  of 
combustion  need  not  exceed  that  stated  above,  the  amount  of  coal 
required  may  be  computed  most  readily  by  basing  it  directly  on 
the  grate  surface.  With  a  climate  like  that  in  many  sections  of 
the  northeastern  part  of  this  country,  where  the  heating  season  is 
of  about  seven  months  duration  and  the  average  outside  tempera- 
ture during  that  time  is  not  far  from  40  to  45  degrees,  the  aver- 
age rate  of  combustion  will  be,  roughly,  from  1^4  to  ij4  pounds 
per  square  foot  per  hour. 

Take,  for  example,  a  boiler  of  medium  size,  in  which  the  coal 
is  to  be  burned  no  faster  than  a  5  pound  rate  in  zero  weather. 
Assume  the  heating  season  to  last  200  days,  or  4,800  hours. 
With  an  average  outside  temperature  of,  say,  45  degrees,  the  aver- 
age rate  of  combustion,  based  on  the  difference  between  the  indoor 

2C 

and  outdoor  temperatures,  will  be  only   —  X  5  —  J-79  pounds. 

Making  allowance  for  the  lower  temperature  maintained  at  night 
brings  the  average  rate  down  to  about  1.68  pounds.  This,  with  a 
boiler  having  4  square  feet  of  grate  surface,  gives  4  X  1.68  X 
4,800  =  32,256  pounds,  or  about  16  tons  for  the  season. 

If  the  estimate  be  based  on  the  radiating  surface  instead  of  on 
the  grate  area,  we  may  assume,  for  example,  a  house  heated  by 
1,000  square  feet  of  direct  radiation,  including  mains  as  a  part  of 
the  surface. 

Using  the  figures  previously  stated — viz.,  150  heat  units  per 
square  foot  of  direct  hot  water  radiating  surface  and  8,000  heat 
units  utilized  per  pound  of  coal,  we  have  1,000  X  150  -r-  8,000  = 
1 8.8  pounds  per  hour  in  coldest  weather.  The  average  hourly  con- 
sumption, with  an  outside  temperature  of  45  degrees,  would  be 

^  X  18.8,  and  the  total  for  the  season  of  4,800  hours-^-  X  18.8 
70  70 

X  4,800  =  approximately  32,200  pounds.    This  would  be  reduced, 


26  Principles    of    Heating. 

owing  to  the  lower  temperature  kept  up  at  night  to,  say,  15  tons. 
With  indirect  radiation,  reduce  to  approximate  equivalent  di- 
rect radiation  by  multiplying  by  not  less  than  1.6.  Some  boiler 
manufacturers  recommend  multiplying  by  1.75.  Expressed  in 
another  way  the  computation  just  made,  based  on  hot  water  radia- 
tion, gives  about  40  pounds  of  coal  per  season  per  square  foot  of 
surface  in  radiators,  allowing  25  per  cent,  for  mains.  With  steam 

2CQ 

radiation    the   coal    required     would    be  —   —  X  40  =  about    70 

pounds. 

It  may  be  well  to  repeat  that  the  above  computations  apply  only 
to  properly  proportioned  systems.  If  a  boiler  is  known  to  be 
small  for  its  work  a  higher  average  rate  of  combustion  must  be 
assumed  and  vice  versa. 

There  is  no  economy  in  having  a  boiler  so  large  that  the  fire 
must  be  checked  by  opening  the  feed  door  or  running  with  a  very 
low  rate  of  combustion. 

With  a  pair  of  boilers  it  is  better  to  run  one  at  its  maximum 
rate  until  the  second  one  is  needed  rather  than  run  both  with 
drafts  checked  nearly  to  the  limit. 


CHAPTER  IV. 
FURNACE    TEST5. 

TESTS    ON     THE    RATE     OF     COMBUSTION     IN     FURNACES     AND    THE 
VELOCITY  OF  AIR  IN   THE  PIPES. 

The  folowing  tests  were  made  on  the  heating  apparatus  in  a 
frame  house  29  by  35  feet,  with  parlor,  dining  room  and  reception 
room  on  the  first  floor,  and  four  bedrooms  and  a  bathroom  on 
the  second  floor,  heated  during  one  winter  season  by  a  brick  lined 
wrought  iron  furnace  with  a  22-inch  fire  pot,  and  during  the  fol- 
lowing season  by  a  cast  iron  furnace  with  a  tapering  fire  pot  hav- 
ing an  average  diameter  of  about  23  inches. 

The  brick  lined  furnace  was  tested  during  a  20  days'  run  in 
midwinter.  The  average  outside  temperature  during  this  period, 
based  on  readings  taken  night  and  morning,  was  26.3  degrees; 
total  weight  of  coal  burned,  2,328  pounds ;  rate  of  combustion  per 
square  foot  of  grate  per  hour,  1.84  pounds.  A  cold  day  run  was 
made  a  little  later  in  the  season,  the  thermometer  ranging  from  7 
degrees  below  zero  to  8  degrees  above.  During  the  24  hours  test 
coal  was  fed  six  times,  the  total  weight  amounting  to  258  pounds, 
making  the  average  rate  of  combustion  4.07  pounds  per  square 
foot  of  grate  per  hour. 

The  cast  iron  furnace  was  tested  during  a  32  days'  trial,  the 
average  outside  temperature  based  on  three  readings  per  day, 
being  27^2  degrees.  The  total  weight  of  coal  burned  was  4,350 
pounds ;  the  average  per  square  foot  of  grate  per  hour  being  1 .97 
pounds.  During  this  test  a  record  of  room  temperatures  was 
kept,  the  average  being  fully  70  degrees. 

A  COLD  DAY  TEST. 

During  this  test  a  particularly  severe  day  occurred,  the  tem- 
perature falling  to  12  below  zero.  The  coal  burned  during  these 
24  hours  amounted  to  300  pounds,  giving  an  average  rate  of  4.35 
pounds  per  square  foot  of  grate  per  hour.  Coal  was  fed  seven 
times.  The  fire  pot  was  red  hot  while  the  thermometer  remained 

27 


28  Principles    of    Heating. 

below  zero.  The  weight  of  ashes  and  unconsumed  fuel  passing 
through  the  grate  was  10  per  cent,  of  the  weight  of  Lehigh  egg 
coal  supplied.  The  house  in  which  these  furnaces  were  installed 
was  of  ordinary  frame  construction,  shingled  on  building  paper 
and  plastered  inside.  The  total  cubic  contents  of  rooms  connected 
with  the  furnace  was  11,674  cubic  feet.  The  total  combined  ex- 
posed wall  and  glass  surface  was  1,683  square  feet. 

It  is  to  be  noted  that  both  furnaces  used  were  inside  the  aver- 
age rating  given  by  reputable  manufacturers  to  furnaces  of  their 
size — namely,  about  14,000  cubic  feet.  If  based  on  the  exposure 
such  furnaces  are  expected  to  carry  approximately  1,700  square 
feet  of  combined  wall  and  glass  surface  when  the  latter  does  not 
exceed,  say,  one-sixth  the  total  exposure.  The  exposure  in  this 
case  is  practically  the  same  as  the  above  figure.  The  house  had 
storm  windows  on  the  north  and  west  sides,  yet  an  average  rate 
of  combustion  of  nearly  5  pounds  per  square  foot  of  grate  per 
hour  was  found  necessary  to  keep  the  rooms  comfortable  in  se- 
vere weather.  This  high  rate  requires  pretty  frequent  attention 
and  should  be  considered  a  maximum. 

DATA   ON   SIZE   OF  ROOMS,    PIPES,   AND   THE   FLOW   OF   AIR. 

The  dimensions  and  other  data  of  the  several  rooms  are  as 
follows : 

TABLE  II. 

ANEMOMETER   TESTS. FURNACE    HEATING. 

Approximate  Diam. 

Rooms.  contents.  Sides  Size  of  of 

First  floor.                  Dimensions.— Feet.  Cubic  feet,  exposed,  register.  pipe. 

Dining    room 13    '  x  18  x  8V2  2,000  2  10  x  14  10 

Parlor    14%  x  15  x  814  1,850  2  10  x  14  10 

Hall    14     x  18  x  Sy2  2,140  2  10  x  14  10 

Second  floor. 

Bedroom    9  x  12     x  8  864  2  8  x  12  1 

Bedroom     10  x  19     x  8  1,520  2  8x12  8 

Bedroom     10  x  12     x  8  960  1  8  x  12  7 

Bedroom    13  x  13     x  8  1,350  2  9  x  12  8 

Bath     6  x    7%  x  8  390  1  7  x  10  6 


11,674 

Anemometer  tests  were  made  with  the  following  results  : 
Temper- 
ature at        Velocity  Hori- 

Room.                    register.         in  pipe.          Size  pipe,  zontal  run.      /—Elbows.-^ 

First  floor,                Deg.  F.              Feet.              Inches.  Feet.            90°            45° 

Dining    room 116                  418                  10  8                  1                  1 

Parlor    114                  429                  10  2                ..2 

Hall     146                  465                  10  4                  1                  1 


Furnace    Tests.  29 

Temper- 
ature at  Velocity  Hori- 

Room.                    register.  in  pipe.  Size  pipe,  zontal  run.  , — Elbowg. — N 

Second  floor.                Deg.  F.             Feet.  Inches.       Feet..  90°  45° 

Bedroom    100                  252  7  16  2                  2 

Bedroom    104                  320  8  12  2                  2 

Bedroom    104                  510  7211 

Bedroom    127                  570  8  2  1                  1 

Bath     103                  286  6  8  1                  1 

The  above  tests  were  made  with  cold  air  box  wide  open  and 
with  little  or  no  wind.  The  outside  temperature  was  5  degrees. 
The  register  temperatures  were  lower  than  would  have  been  nec- 
essary to  keep  the  rooms  comfortable  had  it  not  been  that  they 
had  been  warmed  to  a  temperature  considerably  in  excess  of  70 
degrees,  and  furnace  drafts  were  checked  to  reduce  the  heat. 

Other  tests  were  made,  closing  all  registers  on  the  first  floor, 
giving  velocities  of  over  500  feet  in  the  rooms  on  the  second  floor 
most  remote  from  the  furnace.  Tests  were  made  in  34  degree 
weather,  showing  a  velocity  of  only  about  280  feet  in  rooms  on 
the  first  floor.  Anemometer  readings  taken  in  the  cold  air  box 
showed  a  velocity  of  over  300  feet  and  a  volume  of  900  to  980 
cubic  feet  per  minute,  corresponding  to  an  air  change  in  the  rooms 
heated  once  in  about  13  minutes. 

OTHER  TESTS. 

Tests  made  in  another  house  with  outside  temperature  24  de- 
grees showed  velocities  in  pipes  leading  to  the  first  floor  ranging 
from  306  to  334  feet,  the  temperature  at  the  registers  ranging 
from  104  to  109  degrees.  Pipes  leading  to  the  second  floor 
showed  velocities  in  excess  of  450  feet  per  minute  with  slightly 
lower  register  temperatures  than  on  the  first  floor.  The  furnace 
in  this  case  had  a  22  inch  fire  pot.  The  total  volume  of  air  sup- 
plied to  the  house  per  minute  was  850  cubic  feet. 

Stilf  another  test,  made  in  a  different  house,  gave  these  re- 
sults for  rooms  located  on  the  second  and  third  floors,  the  test 
being  made  in  cold  winter  weather.  It  will  be  noted  that  the  reg- 
ister temperatures  in  this  case  are  much  higher  than  in  the  pre- 
vious tests: 


30  Principles    of   Heating. 

TABLE  III. 

FI.UE    VELOCITIES. FURNACE    HEATING. 

Temperature  of  Velocity  Hori- 

entering  air.  in  pipe.  Size  pipe.  zontal  run. 

Room.                             Deg.  F.  Feet.  Inches.  Feet.    Elbows. 

Parlor 138  250  6x10  oval.  9  3 

Library     120  210  6  x  7%  oval.  4  2 

Dining    room 140  275  7  diameter.  15  2 

Hall    151  450  6x8  oval.  7  2 

Bath    108  280  6  diameter.  8  2 

Bedroom     152  500  4Va  x  7V2  oval.  4  3 

Rear   bedroom 140  540  5x7  oval.  12  3 

These  tests  give  only  a  general  idea  of  what  velocities  may  be 
expected  under  ordinary  working  conditions.  From  the  above 
and  other  data  the  writer  has  adopted  these  velocities  in  making 
furnace  heating  computations. 

Approximate  velocity  in  pipes  leading  to  first  floor,  280  feet 
per  minute ;  to  second  floor,  400  feet  per  minute ;  to  third  floor, 
500  feet  per  minute. 

During  the  test  made  in  weather  12  degrees  below  zero  the 
temperature  of  the  air  delivered  by  the  furnace  was  113  to  115 
degrees.  When  the  outside  temperature  rose  to  6  or  8  below 
zero  122  degrees  were  indicated  by  the  thermometer  placed  at 
register  nearest  the  furnace.  The  maximum  increase  in  tempera- 
ture noted  was  130  degrees.  The  wind  was  blowing  strongly  into 
a  wide  open  cold  air  box.  Had  this  been  partially  closed  the  max- 
imum temperature  would  doubtless  have  exceeded  140  degrees, 
which  is  commonly  used  as  a  basis  for  computations  in  work  of 
this  kind. 

ADVANTAGES   OF   AIR   SUPPLY   AT   RELATIVELY   LOW   TEMPERATURES. 

There  are  advantages  in  supplying  air  at,  say,  120  degrees  in 
zero  weather.  There  is  less  tendency  for  the  air  to  remain  at  the 
ceiling  than  when  admitted  at  a  higher  temperature,  thus  pro- 
moting a  better  circulation  in  the  room  and  a  nearer  approach  to  a 
uniform  temperature  throughout.  On  the  other  hand,  the  lower 
the  temperature  of  the  air  supply  the  greater  must  be  the  volume 
to  supply  the  number  of  heat  units  necessary  to  make  good  the 
loss  through  exposed  walls  and  glass,  consequently  the  more  fre- 
quent the  air  ch?.nge  and  the  greater  the  fuel  consumption. 


CHAPTER  V. 

SPECIFIC  HEAT,  THE  HEATING  AND  COOLING 
OF 'AIR  AND  HUMIDITY. 

SPECIFIC   HEAT   AND   THE   HEATING   AND   COOLING  OF   AIR. 

Different  substances  vary  greatly  in  the  amount  of  heat  they 
must  absorb  to  raise  their  temperature  a  given  amount.  The  quan- 
tity of  heat  that  must  be  imparted  to  a  body  to  raise  its  tempera- 
ture i  degree  in  comparison  with  that  required  to  raise  an  equal 
weight  of  water  i  degree  is  known  as  the  "  specific  heat "  of  the 
body.  Thus,  the  specific  heat  of  air  is  0.2375  (generally  taken  as 
0.238) — that  is,  only  about  one-fourth  as  many  heat  units  are  re- 
quired to  raise  i  pound  of  air  i  degree  as  would  be  necessary  to 
raise  i  pound  water  the  same  amount.  The  specific  heat  of  water 
varies  slightly,  but  this  need  not  be  taken  into  consideration  ex- 
cept for  scientific  work. 

To  determine  how  many  heat  units  are  required  to  heat  a  given 
volume  of  air  a  stated  number  of  degrees  the  quickest  method  is 
probably  to  multiply  the  volume  in  cubic  feet  by  the  degrees  rise  in 
temperature  and  divide  the  product  by  55,  this  number  represent- 
ing approximately  the  number  of  cubic  feet  of  air  at  70  degrees 
that  will  be  raised  i  degree  by  one  heat  unit.  One  cubic  foot  of 
dry  air  at  70  degrees  temperature  weighs  0.0747  pound,  or  i 

pound  occupies  13.4  cubic  feet.     One  heat  unit  will  raise g 

pound  of  air  i  degree,  equal  to  4.2  pounds  of  air  i  degree.  Since 
i  pound  of  dry  air  occupies  13.4  cubic  feet,  i  heat  unit  will  raise 
4.2  X  134  cubic  feet  i  degree  =  56  cubic  feet;  55  cubic  feet  is 
commonly  used  in  making  approximate  calculations.  On  pre- 
cisely the  same  basis  it  will  be  found  that  i  heat  unit  will  raise 
approximately  50  cubic  feet  of  air  at  zero  through  I  degree,  zero 
air  weighing  0.0864  pound  to  the  cubic  foot. 

31 


32  Principles  of  Heating. 

TABLE   IV. 

THE   WEIGHT  OF  AIR  PER  CUBIC   FOOT  AT  DIFFERENT   TEMPERATURES. 

Weight  in  Weight  in 

pounds  of  pounds  of 

Tempera-                               1  cubic  foot  Tempera-                                      1  cubic  foot 

ture. — F.                                    of  dry  air.  ture. — F.                                          of  dry  air. 

0 0.0864  92 0.0720 

12 0.0842  102 0.0707 

22 0.0824  112 0.0694 

32 0.0807  122' 0.0682 

42 0.0791  132 0.0671 

52 0.0776  142 • 0.0660 

62 0.0761  152 0.0649 

72 0.0747  162 0.0638 

82 0.0733 

COOLING  AIR. 

When  the  volume  of  air  to  be  cooled  is  small,  ice  is  generally 
used,  each  pound  in  melting  absorbing  about  142  heat  units.  Sup- 
pose, for  example,  it  is  desired  to  know  the  weight  of  ice  that 
must  be  melted  to  cool  60,000  cubic  feet  of  air  per  hour  from  90 
down  to  80  degrees,  the  water  from  the  melted  ice  to  be  dis- 
charged at  62  degrees  temperature : 

Heat  units. 

1  pound  of  ice,  in  melting,  absorbs 142 

1  pound  of  water,  when  warmed  from  32°  to  62°,  absorbs 30 

Total   heat  units  absorbed 172 

One  cubic  foot  of  air  at  90  degrees  weighs  0.072  pound.  Hence 
60,000  cubic  feet  will  weigh  4,320  pounds.  Since  the  specific  heat 
of  air  is  0.238,  the  number  of  heat  units  that  must  be  absorbed  by 
melting  ice  to  cool  this  weight  of  air  10  degrees  will  be  4,320 
pounds  X  10  X  0.238  —  10,250  heat  units,  approximately.  Since 
i  pound  of  ice  melted  and  the  water  raised  to  62  degrees  absorbs 
172  heat  units,  10,250  -4-172  heat  units  will  be  required,  equal  to 
about  60  pounds  of  ice  per  hour  to  cool  60,000  cubic  feet  of  air  10 
degrees  F. 

The  ice  would  be  most  effective  if  it  were  crushed  into  small 
pieces  so  that  the  air  would  come  in  close  contact  with  it.  This, 
unfortunately,  would  seriously  retard  the  flow  of  air,  owing  to 
the  increased  resistance  over  that  when  large  cakes  are  used.  With 
the  latter  arranged  in  properly  constructed  racks  and  provision 
made  for  retaining  the  water  until  its  temperature  has  increased 
to  within  20  or  30  degrees  of  that  of  the  air,  good  results  have 


Hea.ting    and    Cooling    of   Air.  33 

been  obtained ;  but  practically  one  must  expect  the  amount  of  ice 
required  to  exceed  considerably  the  theoretical  weight  based  on 
the  volume  of  air  cooled,  since  there  are  losses  by  transmission 
through  surrounding  partitions,  walls,  etc. 

For  large  systems  mechanical  refrigeration  should  be  used.  It 
may  be  said  in  a  general  way  that  in  small  plants  the  consumption 
of  i  ton  of  coal  is  sufficient  to. produce  7  to  8  tons  of  commercial 
ice.  The  actual  ice  making  capacity  of  a  machine  is  only  50  to  60 
per  cent,  of  its  ice  melting  capacity,  which  is  expressed  in  tons 
capacity  in  24  hours — that  is,  a  3O-ton  machine  means  a  refriger- 
ating capacity  in  24  hours  equivalent  to  that  produced  by  the 
melting  of  30  tons  of  ice.  The  machine  would  produce,  however, 
only  15  to  1 8  tons  of  real  ice  in  the  same  period.  For  cooling  air 
with  a  refrigerating  plant,  brine  at,  say,  8  to  12  degrees  F.  would 
be  circulated  by  pumps  through  coils  over  which  the  air  would  be 
required  to  pass. 

Unfortunately,  the  cooling  of  air  does  not  make  it  agreeable. 
Its  relative  humidity  is  increased,  which  makes  it  less  capable  of 
absorbing  moisture  or  perspiration  from  the  body.  Therefore  the 
air  should  be  dried  by  passing  it  over  trays  of  calcium  chloride, 
which  has  a  great  capacity  for  absorbing  moisture,  or  it  may  be 
slightly  heated  after  the  chilling  process  to  reduce  its  humidity. 

MECHANICAL  EQUIVALENT  OF  HEAT. 

A  definite  relation  exists  between  work  and  heat.  The  unit  of 
work  is  the  foot-pound — viz.,  the  work  required  to  raise  I  pound 
i  foot.  It  has  been  determined  experimentally  that  I  heat  unit  is 
equivalent  to  778  foot-pounds. 

Whenever  mechanical  work  is  done  heat  is  given  off.  Thus, 
the  heat  due  to  the  running  of  machines  in  a  shop  assists  in  the 
warming  of  the  room.  A  horse-power  is  33,000  foot-pounds  per 
minute.  For  each  mechanical  horse-power  expended  in  whatever 
manner  in  factory,  shop  or  elsewhere,  33,000  -=-  778  =  42.4  heat 
units  are  given  off.  A  mechanical  horse-power  hour  is  equal,  then, 
to  2,544  heat  units  per  hour,  an  amount  equal  to  the  loss  of  heat 
through  over  30  square  feet  of  glass,  or  that  given  off  by  8  to  10 
square  feet  of  direct  radiation. 


34  Principles  of  Heating. 

EVAPORATION  AND  HUMIDITY. 

To  moisten  air  water  must  be  evaporated  or  steam  must  be 
injected  into  it.  In  either  case  about  1,000  heat  units  are  necessary 
for  the  evaporation  of  I  pound  of  water  or  the  making  of  I 
pound  of  steam.  Water  evaporates  very  slowly  when  exposed  in 
still  air,  the  evaporation  per  square  foot  from  a  water  surface  in 
contact  with  still  air  at  70  degrees  having  a  relative  humidity  of 
40,  being  about  1-40  pound  per  hour.  The  rate  of  evaporation 
rapidly  increases  with  an  increase  in  temperature  or  the  passage 
of  air  across  the  surface  of  the  water.  The  capacity  of  air  to 
absorb  moisture  increases  rapidly  with  its  rise  in  temperature — 
e.  g.,  air  at  70  degrees  can  absorb  about  four  times  as  much  mois- 
ture as  air  at  30  degrees,  as  will  be  seen  by  referring  to  Table  V : 

TABLE  v. 

THE  WEIGHT  OF   WATER  VAPOR  PER   CUBIC   FOOT  OF   SATURATED   SPACE  AT   DIFFERENT 

TEMPERATURES. 

Weight  of  Weight  of 

Tern-                  vapor  in  grains  Tern-                    vapor  in  grains 

perature.              per  cubic  foot.  perature.                  per  cubic  foot. 

0 0.54  50 4.09  =    4  approz. 

10 0.84  60 5.76 

15 0.99  =  1  approx.  70 7.99  =    8  appro*. 

20 1.30  80 10.95 

30 1.97  =  2  approx.  90 14.81 

40 2.88  100 19.79  =  20  approx. 

1  pound  avoirdupois  =  7000  grains. 

Approximately  1000  heat  units  are  required  to  evaporate  1  pound  of  water. 

The  amount  of  heat  and  fuel  necessary  to  moisten  air  is  not 
generally  appreciated.  To  illustrate  this  point  take  the  amount  of 
heat  required  to  moisten  air  entering  a  furnace  at  30  degrees,  with 
a  relative  humidity  of  65,  so  that  a  relative  humidity  of  50  will  be 
maintained  in  the  rooms  kept  at  70  degrees.  Assume  that  50,000 
cubic  feet  of  air  per  hour  passes  through  the  furnace :  One  cubic 
foot  of  saturated  air  at  30  degrees  temperature  contains,  approxi- 
mately, 2  grains  of  moisture,  and  with  a  relative  humidity  of  65 
would  contain  1.3  grains.  Each  cubic  foot  of  air  at  30  degrees 
expands  to  1.08  cubic  feet  when  heated  to  70  degrees.  One  cubic 
foot  of  saturated  air  at  70  degrees  contains  about  8  grains  of 
moisture.  With  50  relative  humidity  I  cubic  foot  of  7o-degree 
air  would  contain  4  grains. 

The  amount  of  moisture  that  must  be  supplied  by  the  evaporat- 
ing pan  in  the  furnace  is  the  difference  between  50,000  cubic  feet 


Heating    and    Cooling    of   Air.  35 

per  hour  X  1.08  X  4  and  50,000  X  1.3.  The  difference  equals 
151,000  grains,  or  21.6  pounds,  per  hour.  Since  about  1,000  heat 
units  are  required  to  evaporate  I  pound  of  water,  21,600  heat  units 
per  hour  are  absorbed,  equal  to  the  heat  utilized  from  the  burning 
of  about  2.y2  pounds  of  coal. 

The  effect  of  an  ordinary  evaporating  pan  is  of  slight  conse- 
quence in  moistening  the  large  volume  of  air  that  passes  through 
a  furnace.  If  an  attempt  is  made  by  specially  provided  means  to 
raise  the  relative  humidity  in  the  room  to,  say,  50,  in  cold  winter 
weather,  the  moisture  will  condense  on  the  windows  and  they  will 
become  frosted.  A  relative  humidity  of  about  30  is  said  to  be  as 
high  as  one  can  secure  without  this  trouble  from  condensation. 


CHAPTER  VI. 
HEAT  GIVEN  OFF  BY  DIRECT  RADIATORS  AND  COILS. 

Repeated  tests  have  shown  the  amount  of  heat  given  off  by 
ordinary  cast  iron  radiators  per  square  foot  of  heating  surface 
per  hour  per  degree  difference  in  temperature  between  the  steam 
or  water  in  the  radiator  and  the  air  surrounding  same  to  be  about 


PLAN 


Fig.  16. — Plan  and  Front  and  Side  Elevations,  Showing  Method  of  Concealing 
Radiator  with  Marble  Wainscoting. 

1.6  heat  units.  With  this  as  a  basis  a  steam  radiator  under  5 
pounds  pressure,  corresponding  to  228  degrees,  surrounded  by  air 
at  70  degrees  (neglecting  the  difference  in  temperature  between 
the  air  near  the  top  and  the  bottom  of  the  radiator),  will  give  off 
(228  —  70  degrees)  X  1.6  heat  units  per  square  foot  per  hour  = 
253,  commonly  taken  as  250.  With  hot  water  at  an  average  tem- 
perature of  160  the  heat  given  off  is  (160  —  70)  X  1.6  =  144, 
commonly  taken  at  150. 

36 


Heat  Given  Off  by  Direct  Radiators  and  Coils.  37 

These  are  good  average  figures  to  use.  If  we  go  into  the  sub- 
ject closely  we  note  that  low  radiators  are  more  effective  than 
high  ones  and  those  of  single  column  pattern  are  more  effective 
than  deeper  radiators,  since  they  radiate  their  heat  more  freely 
and  air  will  circulate  around  them  to  better  advantage. 

Wall  radiators  and  coils  of  pipe  are  still  more  effective,  over- 
head coils,  with  pipes  side  by  side,  giving  off  more  heat  per  square 
foot  than  those  on  walls  with  the  pipes  one  over  the  other.  The 
advantage  in  the  location  of  the  latter,  however,  more  than  offsets 
the  greater  efficiency  of  those  placed  overhead,  as  is  common  in 
mill  heating.  Coils  may  be  based  on  300  to  350  heat  units  per 
square  foot  per  hour  with  low  pressure  steam,  and  wall  radiators 
on  about  the  same  amount.  Concealed  radiators,  like  the  one 
illustrated  in  Fig.  16,  give  off  practically  no  heat  by  radiation, 
but  heat  the  room  by  heating  the  air  passing  over  them — that 
is,  by  convection.  Such  radiators  should  therefore  be  rated  to 
give  off  not  more  than  200  heat  units  per  square  foot  per  hour, 
depending  on  the  hight  and  arrangement. 

NOTES  ON   HEAT  EMITTED  BY  DIRECT   RADIATORS. 

Professor  Carpenter,  in  Vol.  I,  Transactions  A.  S.  H.  &  V.  E., 
states :  "  The  capacity  for  heat  transmission  increases  at  a  much 
higher  rate  than  the  difference  of  temperature.  The  efficiency  of 
the  radiator  will  be  greatly  increased  by  increasing  the  steam 
pressure  or  by  forcibly  bringing  the  air  in  contact  with  it.  The 
heat  emitted  per  hour  under  different  conditions  by  the  same 
radiator  was  found  by  tests  to  vary  about  15  per  cent.,  this  varia- 
tion being  largely  due  to  a  difference  in  temperature  and  also  to 
changes  in  velocity  of  air  passing  over  the  radiator. 

"  With  radiators  of  the  same  form,  but  of  different  heights,  the 
lower  the  radiator  the  more  efficient.  In  the  case  of  a  Royal 
Union  radiator  17  inches  high,  with  practically  the  same  amount 
of  heating  surface  as  another  37  inches  high,  50  per  cent,  more 
heat  was  emitted  by  the  low  radiator.  The  radiator  coefficient 
for  a  difference  of  temperature  of  150  degrees  is  usually  about 
1.6  heat  units;  that  for  a  2-inch  horizontal  pipe  3.8  heat  units; 
i-inch  pipe,  5.7  heat  units. 

"  Radiators  with  one  row  of  tubes  are  much  superior  to  those 
of  the  same  kind  with  two  or  more  rows  of  tubes.  The  fact  that 


38  Principles  of  Heat  in 


<r 


low  radiators  are  more  efficient  than  high  ones  would  indicate  that 
the  tubes  in  the  high  radiators  are  too  closely  placed ;  that  the  air 
in  its  passage  upward  reaches  nearly  its  maximum  temperature  in 
a  short  distance  and  from  that  point  upward  absorbs  but  little 
heat." 

The  average  of  many  tests  on  ordinary  cast  iron  radiators  ap- 
pears to  confirm  the  figure  of  1.6  heat  units  per  square  foot  an 
hour  per  degree  difference  in  temperature  as  a  fair  one  to  use. 

Tests  made  by  the  City  Engineer  of  Richmond,  Va.,  on  several 
types  of  radiators  commonly  used,  gave  results  ranging  from  1.43 
heat  units  to  1.81  heat  units  per  square  foot  an  hour  per  degree 
difference  in  temperature.  The  average  of  the  tests  on  five  dif- 
ferent makes  of  radiators  was  1.68. 

Monroe,  in  his  book  on  "  Steam  Heating  and  Ventilation  " 
states :  "  The  writer  found  that  under  the  conditions  in  his  test- 
ing plant  the  38-inch,  2-column  cast  iron  radiator  gave  out  1.6 
heat  units  per  square  foot  per  hour  per  degree  difference  of  tem- 
perature, with  an  average  difference  of  147.5  degrees." 

He  states  that  "  within  the  limits  of  ordinary  radiator  practice 
with  steam  temperatures  from  212-230  degrees,  and  mean  air 
temperatures  from  40-70  degree,  the  coefficient  of  1.6  will  not 
vary  more  than  9  per  cent,  due  to  the  difference  in  temperature 
between  the  steam  and  air.  The  radiator  which  has  the  most  open 
space  around  its  surface  and  the  largest  uninterrupted  exposure 
to  the  surrounding  air  will  give  out  the  most  heat  per  square  foot 
under  the  same  conditions.  In  compliance  with  this  rule,  other 
things  being  equal,  narrow  radiators  are  more  effective  than 
wide  ones  and  low  ones  than  high  ones.  Professor  Cooley  found 
that  a  single  coil  of  horizontal  pipes  set  side  by  side  gives  out  40 
per  cent,  more  heat  per  square  foot  than  a  two  column  cast  iron 
radiator  under  the  same  conditions." 

In  the  "  Plumbers'  and  Fitters'  Pocket  Book,"  published  by 
the  International  Correspondence  Schools,  1905,  a  statement  is 
made  that  the  heat  units  emitted  per  hour  per  square  foot  of  sur- 
face per  degree  difference  in  temperature  amounts  with  90  degrees 
difference  (which  would  correspond  approximately  with  hot 
water  heating  conditions),  to  1.41  for  radiators  40  inches  high, 
1.7  for  radiators  24  inches  high,  1.62  for  single  column  radiators 


Heat  Given   Off  bv  Direct  Radiators  and  Coils. 


39 


40  inches  high,  and  2.22  for  those  24  inches  high.  The  figures 
taken  in  the  same  order  for  over  160  degrees  difference  in  tem- 
perature corresponding  practically  to  steam  heat  conditions  would 
be  1.66,  1.98,  1.88  and  2.59. 

The  Fowler  &  Wolfe  Mfg.  Co.'s  catalogue  gives  a  summary 
of  tests  as  follows : 

TABLE  VI. 

Summary  of  Tests  of  various  steam  radiators  made  at  Sibley  College,  Cornell 
University,  by  Messrs.  Camp,  Woodward  and  Sickles,  mechanical  engineers,  under 
the  direction  of  R.  C.  Carpenter,  M.S.C.E.,  M.M.E.  (This  summary  is  the  aver- 
age  of  several  consecutive  tests  made  on  these  several  radiators.) 

A  standard 
These  tests  were 
all     made     in 
the  same  closed 

Standard 

hight  3- 

column  cast 

iron  radiator. 


A  stand- 
ard hight 
cast  iron 
radiator 
with  loops 
attached 
to  base. 


F.  &  W. 

room  under  even    wall  radia- 

temperatures      tor.   Stand- 

and  under  same      ard  7-foot 

conditions.  section  tested. 

*B.  T.  U.    heat    radiated 

per    hour    per    square 

foot  of  actual  surface. 

Pev   degree   difference 

in    temperature 2.325  1.732  1.705 

B.  T.  U.  heat  radiated  per 
hour  per  rated 
square  foot  of  sur- 
face. Per  degree  dif- 
ference in  tempera- 
ture   2.400  1.712  1.594 

Steam  condensed  per 
hour  per  actual 
square  foot  of  heat- 
ing surface.  Pounds.  0.351  0.236  0.239 


hight  radia- 
tor made  of  1- 
inch  wrought 
iron  pipe  at- 
tached to  cast 

Iron  base 
3  rows  wide. 


A  stand- 
ard hight 

cast  iron 
2-column 

radiator. 


1.643 


1.266 


0.182 


1.319 


1.266 


0.182 


B.T.U.  —  British  thermal  units,  or  heat  units. 


Reference  is  made  in  the  Heine  Safety  Boiler  Co/s  catalogue 
to  the  average  of  four  experiments  on  the  condensation  in  uncov- 
ered pipes  which  showed  with  an  average  steam  pressure  of  5 
pounds  gauge,  2.236  heat  units  per  square  foot  per  hour  per  I 
degree  F.  Other  tests  showed  a  loss  of  2.812  for  bare  pipe. 

Mr.  A.  R.  Wolff  gives  250  heat  units  per  square  foot  per  hour 
for  ordinary  cast  iron  radiators  with  steam  from  3  to  5  pounds 
per  square  inch,  and  recommends  about  60%  of  this  amount  for 
hot  water  heating. 

The  results  of  a  number  of  radiator  tests  are  given  in  Mills's 
book  on  "  Heating  &  Ventilation,"  Vol.  II.,  page  335.  The  heat 


4°  Principles    of   Heating. 

emitted  from  cast  iron  radiators,  according  to  these  tests,  ranges 
from  1.4  for  certain  types  of  cast  iron  radiator,  to  2.38  for  single 
column  wrought  iron  tube  radiator.  Heat  given  off  by  horizontal 
pipes  is  as  follows :  i-inch  pipe  2.73 ;  2-inch  pipe  2.3 ;  3-inch  pipe 
2-33. 

The  following  figures  are  taken  from  "  Steam  in  Covered  and 
Bare  Pipes,"  by  Paulding: 

TABLE  VII. 

LOSS    OF    HKAT    FKOM    PIPKS. 


Name  of 
experimenter. 
Barrus                               .  . 

T< 
Size  of  pipe. 
Inches. 
2 

imperature 
of  steam. 
Deg.  F. 
325.2     • 
365.4 
365.3 
358.0 
354.7 
300.6 
344.5 

Tempera- 
ture 
of  air. 
Deg.  F. 
56.6 
63.2 
73.6 
67.0 
80.1 
71.2 
75.5 

B.  T.  U. 

per  square 
foot  per  hour 
per  1  deg. 
3.01 
3.25 
3.18 
3.10 
3.13 
2.78 
2.71 

Barrus 

.      2 

Barrus 

.  .10 

•Hudson-Beare 

3.53* 

130    pounds 

...    2 

Jacobus                   •  • 

2 

Brill    . 

.    8 

*  Actual  outside  diameter. 

Since  the  heat  given  off  is  roughly  proportional  to  the  differ- 
ence in  temperature  between  the  steam  and  the  air  in  the  room, 
radiators  placed  in  rooms  to  be  heated  to  a  temperature  lower 
than  70  degrees,  say  50  degrees,  will  give  off  with  radiators  at 

228  degrees  ~ — ~ — ^-~  X  250  heat  units  —  about  280  heat  units. 

In  this  connection  it  may  be  well  to  remark  that  in  computing- 
boiler  capacity  one  must  remember  that  catalogue  ratings  are 
based  on  the  radiators  being  placed  in  rooms  at  70  degrees.  The 
radiation  must  be  reduced  to  equivalent  surface  when  surrounded 
by  air  at  70  degrees  temperature. 

It  has  just  been  shown  that  in  rooms  at  50  degrees  the  radi- 
ators give  off  280  heat  units,  against  250  heat  units  in  7o-degree 
rooms ;  hence,  a  boiler  rated  for,  say  2500  square  feet  will  carry 

only  °  X  2500  =  2230  square  feet  if  the  rooms  are  to  be 
heated  to  only  50  degrees. 

HEAT    GIVEN    OFF    BY    INDIRECT    RADIATORS. 

Indirect  radiators  of  the  pin  or  similar  type,  with  extended 
surface,  arranged  somewhat  as  shown  in  Fig.  17,  give  off  heat  not 


Heat  Given  Off  by  Direct  Radiators  and  Coils.  41 

only  in  proportion  to  the  difference  in  temperature  between  the 
steam  and  the  surrounding  air,  but  in  proportion  (though  not  di- 
rectly) with  the  volume  of  air  coming  in  contact  with  them. 

The  tests  made  some  years  ago  by  John  H.  Mills  have  been 
frequently  quoted  by  writers  on  heating  and  ventilation.  The 
writer  has  reduced  these  tests  to  a  zero  basis  for  the  entering  air, 
the  data  being  given  in  the  following  table. 

TABLE  VIII. 

THE  HEAT  UNITS  GIVEN  OFF  PER  SQUARE  FOOT  PER  HOUR  FROM  INDIRECT  PIN 
RADIATORS  HAVING  40  PER  CENT.  PRIME  SURFACE. STEAM,  5  POUNDS  PRES- 
SURE !  ENTERING  AIR,  0  DEGREE  F. 

Velocity    in   feet    per 
minute    between  10 
square   foot   sec- 
Cubic  feet  of  air  per  Heat  units  t  i  o  n  s,    having    % 
hour  passing  over                         given  off  per  hour  square  foot  air  space 
each,  square  foot  of                         per  square  foot  of  between     each    two 
heating  surface.                            extended  surface.  sections. 

100  370  50 

200  540  100 

300  7.00  150 

400  850  200 

500  1,015  250 

600  1,175  300 

700  1,330  350 

800  1,500  400 

It  is  common  to  assume  about  400  heat  units  to  be  given  off 
per  square  foot  an  hour  from  ordinary  indirect  pin  radiators  with 
low  pressure  steam.  Short  vertical  flues  mean  low  velocities; 
higher  ones  give  an  increased  air  flow. 

The  table  shows  that  where  a  good  velocity  between  the  sec- 
tions may  be  secured  their  effectiveness  is  increased  and  less  sur- 
face is  required. 

COMPUTING  INDIRECT  RADIATING  SURFACE. 

To  illustrate  the  use  of  the  table,  suppose  we  have  a  room 
20  X  30  X  12  which  it  is  desired  to  heat  by  indirect  radiation  and 
change  the  air  every  12  minutes — contents  equals  7200  cubic  feet. 
With  5  changes  per  hour  36,000  cubic  feet  must  be  supplied. 
The  heat  loss  by  transmission,  with  two  sides  exposed,  would  be 
about  24,000  heat  units  per  hour.  The  loss  by  ventilation  would 
be  36,000  X.  1/4  (J/4  representing  the  heat  units  carried  away 
by  each  cubic  foot  of  air  escaping  from  a  7o-degree  room,  with 
outside  air  at  o  degree)  =  45,000.  Adding  these,  the  total  heat 
loss  is  81,000  heat  units  per  hour.  Assuming  400  heat  units  per 


42  Principles    of    Heating. 

square  foot  of  radiation  per  hour  gives  a  trifle  over  200  square 
feet  of  surface,  or  a  ratio  of  i  to  36  cubic  feet.  With  36,000  cubic 
feet  per  hour  supplied  the  air  admitted  to  the  indirect  radiators 
would  be  36,000  -:-  200  =  1 80  cubic  feet  per  square  foot  (neglect- 
ing the  difference  in  volume  between  air  at  70  degrees  and  at  o 
degree).  The  table  shows  that  with  200  cubic  feet  per  square 
foot  per  hour  540  heat  units  are  given  off;  hence  we  should  expect 


pjg    17. Indirect  Radiator  Connections. 

that  with  1 80  cubic  feet  about  500  heat  units  in  round  numbers 
would  be  given  off,  in  which  case  only  81,000  -4-  500  =  162 
square  feet  would  be  necessary.  One  must  always  be  certain  that 
the  air  space  through  the  groups  of  radiators  is  considerably  in 
excess  of  the  area  of  flues  connected  therewith.  The  rule  to  allow 
2  square  inches  of  flue  area  to  the  first  floor,  il/2  to  the  second 
floor  and  i%  to  the  third  and  fourth  floors  is  simple,  and  gives 
good  results  in  dwelling  house  work  when  the  radiation  is  prop- 
erly proportioned.  That  is  just  the  difficulty,  however,  for  in  case 
of  a  mistake  in  the  radiation  a  second  mistake  follows  in  the  flues. 


Heat  Given   Off  by  Direct  Radiators  and  Coils. 


43 


Taking  il/2  square  inches  of  flue  area  per  square  foot  of  indi- 
rect radiating  surface  as  a  fair  average  for  a  house,  a  bench  or 
stack  of  zoo  square  feet  would  have  flues  aggregating  150  square 
inches.  The  flue  area  between  the  sections  would  be  about  480 
square  inches,  or  over  three  times  the  flue  area ;  thus,  common 
practice  dictates  that  the  velocity  between  the  sections  of  pin  radi- 
ators shall  be  only  about  one-third  that  in  the  flues.  The  rule  to 
make  the  indirect  surface  50  per  cent,  more  than  the  direct  radi- 
ation that  would  be  required  may  be  shown  on  a  heat  unit  basis 
to  be  very  nearly  true  under  certain  conditions.  For  example, 


THE    METAL    WORKER 


Fig.  18. — Blower  System  Heater. 

take  a  corner  room  16  X  20  X  10  =  3200  cubic  feet,  the  heat 
loss  from  which  is  14,400  heat  units  per  hour.  With  direct  steam 
radiation  rated  at  250  heat  units  14,400  -f-  250  =3  58  square  feet 
would  be  required.  Now,  to  heat  the  same  room  by  indirect  radi- 
ation at  400  heat  units  per  square  foot,  the  air  to  enter  the  room 
at  1 20  degrees,  with  o  degree  outside,  about  86  square  feet  would 
be  required,  computed  as  follows : 

One  cubic  foot  of  air  at  120  degrees  weighs  0.068  pound.  Its 
specific  heat  is  0.238,  therefore  the  heat  units  brought  in  by  a 
cubic  foot  of  air  at  120  degrees  is  0.068  X  120°  X  0.238  =  1.94. 


44 


Principles   of   Heating, 


Of  this  only  -j^-  is  available  to  offset  the  loss  of  heat  by  trans- 
mission, the  other   escaping  with  the  air  leaking  out  at  70 


degrees  temperature. 


50 
1 20 


X  1-94  =  0.810  heat  unit.    To  make 


good  the  loss  of  14,400  heat  units  per  hour  by  transmission  14,400 
~  0.810  =  17,800  cubic  feet  of  air  per  hour  at  120  degrees  must 
be  supplied.  Each  cubic  foot  brings  in  1.94  heat  units;  total 
equals  17,800  X  1.94  =  34>5oo  heat  units,  which  divided  by  400 


THE   METAL   WORKER 

Pig.  19. — A  Heater  for  Blower  Use. 

gives  86,  an  amount  almost  exactly  50  per  cent,  in  excess  of  the 
direct  radiation  required. 

HEAT  GIVEN  OFF  BY  HEATERS  COMBINED  WITH   FANS. 

It  is  not  uncommon  to  secure  an  emission  of  1500  to  2000  heat 
units  or  more  per  square  foot  of  pipe  coils  when  zero  air  is  enter- 
ing the  heater  at  a  velocity  of  1000  to  1200  feet  per  minute,  meas- 
ured between  the  pipes  and  the  steam  is  2  to  5  pounds  gauge 
pressure.  See  Figs.  18  and  19. 

The  heat  given  off  per  square  foot  by  supplementary  heaters 
or  reheaters,  as  shown  in  Fig.  20,  with  which  air  at,  say,  50  to 
70  degrees  from  the  main  tempering  coils  comes  in  contact  would 
be  not  far  from  1000  to  1200  heat  units  in  the  case  of  low  pres- 
sure steam.  The  velocity  of  the  air  and  the  depth  of  heaters — 


Heat  Given  Off  by  Direct  Radiators  and  Coils. 


45 


that  is,  the  number  of  coils  of  pipe  they  contain — have  much  to 
do  with  their  efficiency,  which  depends  chiefly  on  the  steam  pres- 
sure. Assuming  a  main  tempering  coil  arranged  to  have  the  air 
blown  through  it  by  a  fan  or  blower,  as  in  Fig.  21,  or  to  have  the 
air  drawn  through,  as  shown  in  Fig.  22,  to  give  off  2000  heat 
units  per  square  foot  per  hour,  what  amount  of  surface  would 
be  necessary  to  raise  the  temperature  of  30,000  cubic  feet  per 
minute  70  degrees  from  zero? 

Since  one  heat  unit  will  raise  the  temperature  of  approxi- 
mately 50  cubic  feet  of  air  from  o  degree  through  i  degree,  to 


CA9WQ  -~\ 


SUPPLY  HEADER 

ft 


RETURN  HEADER      I 

Fig.  20. — Supplementary  Heater  or  Reheater. 

raise  30,000  X  60  =  1,800,000  cubic  feet  per  hour  70  degrees, 

1,800,000  X  70 
would  require  -  — ±=  2,520,000  heat  units,  which  could 

be  obtained  by  using  a  heater  of  -^—       •    =  1260  square  feet,  or 

2OOO 

about  3600  lineal  feet  of  i-inch  pipe. 

TEMPERATURE    OF    AIR    REQUIRED    TO     HEAT    ROOMS     BY    INDIRECT 

RADIATION. 

It  may  be  desired  to  predetermine  the  temperature  that  must 
be  secured  at  the  air  inlet  to  warm  a  room. 

Take  a  corner  schoolroom,  for  example,  28  x  32  x  12,  with 
30  per  cent,  glass  and  exposed  north  and  west. 

The  equivalent  glass  surface,  rating  the  wall  as  equivalent  to 
one-quarter  as  much  actual  glass  surface,  will  be  342  square  feet. 

The  heat  lost  through  same  per  hour  will  be  342  X  85  X  1.25 
=  36,340  heat  units.  (1.25  being  the  factor  for  N.  or  W.  ex- 
posure.) 

With  the  standard  air  supply  to  a  5o-pupil  room  of  1500  cubic 


46 


Principles    of    Heating. 


feet  per  minute  the  loss  of  heat  by  leakage — that  is,  by  the  re- 
moval of  air  through  the  ventilating  flues — will  be  60  X  1500 
X  i/4  (since  il/4  heat  units  are  removed  by  each  cubic  foot  of 
air  escaping  from  a  room  at  70  degrees  when  the  outside 
temperature  is  at  o  degree)  =  112,500  heat  units  per  hour.  Total 


THE   METAl    WOkKER 


Fig.  21. — A  Fan  Blowing  Air  through  Heater. 

heat  loss  equals  148,840.  To  make  good  the  loss  of  heat  through 
walls  and  glass  the  90,000  cubic  feet  of  air  per  hour  supplied  to 
the  room  (the  volume  being  based  on  7o-degree  temperature) 


THE    METAL   WORKER 


Fig.  22. — Fan  or  Blower  Drawing  Air  through  Heater. 

must  be  superheated  above  the  room  temperature  an  amount 
equivalent  to  the  36,340  heat  units  transmitted  through  walls  and 
glass. 

The  weight  of  90,000  cubic  feet  of  air  at  70  degrees  is  about 
90,000  X  0.075  =  6750  pounds.  The  specific  heat  of  air  is  0.238 
— that  is,  one  heat  unit  will  raise  the  temperature  of  about  4 
pounds  of  air  i  degree. 


Heat  Given  Off  by  Direct  Radiators  and  Coils.  47 

Therefore,  36,340  heat  units  would  raise  the  temperature  of 
36,340  X  4  —  J45>36o  pounds  of  air  i  degree,  or  would  raise  the 


THt   METAL   WOftKI 


Fig.  23. — Section  through  Vent  Flue,   Showing  Aspirating  Coil. 


Fig.  24. — Elevation  on  Line  A  B  of  Fig.  23. 


temperature  of  6750  pounds  of  air;  145,360  -f-  6750  =  about  22 
degrees. 

That  is,  the  air  would  have  to  be  superheated  at  least  22 
degrees  above  the  room  temperature  of  70  degrees  to  maintain 
the  room  at  that  temperature  tinder  the  conditions  stated — viz., 
with  a  change  of  air  about  every  eight  minutes.  As  a  matter  of 


48  Principles    of   Heating. 

fact,  with  the  indirect  system  there  is  a  considerable  difference 
between  floor  and  ceiling  temperatures  in  high  studded  rooms, 
which  means  that  if  70  degrees  is  to  be  maintained  near  the  floor 
a  considerably  higher  temperature  must  be  maintained  above, 
with  a  consequent  increase  in  the  loss  of  heat  by  transmission ; 
therefore,  instead  of  92  degrees,  as  above  computed,  based  on  an 
average  temperature  at  walls  of  70  degrees,  the  inlet  temperature 
would  probably  have  to  be  kept  at  not  less  than  100  degrees  in 
zero  weather,  especially  if  the  windows  were  not  tightly  fitted. 

SIZE  OF  ASPIRATING  HEATERS   OR  COILS. 

To  compute  the  size  of  heaters  or  coils  to  be  placed  in  venti- 
lating flues,  as  shown  in  section  and  elevation  in  Figs.  23  and  24, 
to  produce  an  aspirating  effect  in  a  system  of  ducts,  as  shown  by 
plan  and  elevation  in  Figs.  25  and  26,  we  may  proceed  as  follows : 
Suppose  it  is  desired  to  remove  3000  cubic  feet  of  air  per  minute 
from  a  room.  Knowing  the  size  and  hight  of  the  flue,  for  ex- 
ample, 10  square  feet  area  and  40  feet  high  above  where  the  coil 
is  to  be  placed,  look  up  the  flue  velocities  in  Table  IX — the  excess 
of  temperature  over  that  outdoors  that  must  be  maintained  in  the 
flue  to  produce  the  required  velocity.  In  this  case  the  velocity 
must  be  3000  ~  10  —  300  feet  per  minute,  and  the  excess  tem- 
perature required,  taken  from  Table  IX,  is  20  degrees. 

To  heat  3000  cubic  feet  per  minute  20  degrees  would  require 

3000  X  60  X  20 

—  65,454  heat  units  per  hour  (55  representing 

the  number  of  cubic  feet  of  air  heated  I  degree  by  I  heat  unit). 

With  an  aspirating  heater  made  up  of  ordinary  pin  radiators, 
giving  off,  say,  400  heat  units  per  square  foot  of  extended  sur- 
face per  hour,  and  this  would  be  a  fair  allowance,  the  surface 
required  would  be  65,454  -r-  400  =  163  square  feet.  The  sections 
should  be  coupled  together  with  extra  long  nipples. 

One  should  always  compute  the  air  space  through  heaters  to 
make  sure  it  is  ample. 

The  free  area  between  the  sections  of  the  heater  should  be  at 
least  20  per  cent,  greater  than  the  flue  area,  to  allow  for  the  in- 
creased friction  of  the  air  in  passing  over  the  pins  or  extended 
surface.  A  temperature  rise  of  20  degrees  in  the  ventilating 
flues  to  produce  an  aspirating  effect  would  require  the  use  of  very 


Heat  Given  Off  by  Direct  Radiators  and  Coils.  49 


50  Principles    of    Heating, 

large  heaters  and  coils,  or  radiators.  It  is  therefore  seldom  that 
a  temperature  rise  of  more  than  10  degrees  is  provided  for. 

This  means  that  a  4O-foot  vent  flue  proportionel  to  handle  the 
required  volume  of  air  with  a  2O-degree  excess  of  temperature  in 
the  flue  over  that  outdoors  will  work  without  the  assistance  of 
a  coil  up  to  50  degrees  outside  temperature.  If  the  outdoor  air 
is  60  degrees  then  10  degrees  of  the  20  degrees  excess  is  provided 
"by  the  air  entering  the  vent  flue  from  the  room  at  70  degrees,  the 
balance,  or  other  10  degrees,  to  be  furnished  by  the  aspirating 
•coil. 

Should  the  weather  reach  65  degrees  outside  the  excess  in  the 
flue  would  be  15  degrees,  and  a  slight  falling  off  in  flue  velocity 
would  take  place,  this  falling  off  increasing  as  the  outside  tem- 
perature approaches  70  degrees,  when  windows  may  be  opened 
and  ample  natural  ventilation  secured.  When  possible  it  is  far 
preferable  to  use  a  fan  in  place  of  aspirating  coils  to  produce  the 
desired  removal  of  air.  Positive  results  are  secured  and  the  air 
may  be  handled  at  less  cost. 

It  is  impossible  as  a  rule  to  install  pin  radiators  in  flues  just 
above  the  ventilating  registers  in  rooms  without  cutting  down  the 
flue  area  too  much.  The  radiators  must  therefore  be  placed  in 
the  attic. 

TABLE    IX.* 

THE  APPROXIMATE   VELOCITY   OF  AIR    IN   FLUES   OF   VARIOUS    RIGHTS. 

Outside  temperature,  32  degrees.  Allowance  for  Friction,  50  per  cent,  in  flue  1 

Right  square  foot  in  area. 

of  flue.        , Excess  of  temperature  of  air  in  the  flue  over  that  outdoors. N 

Feet.  10°  20°  30°  40°  50°  60°  70°  80°  90°  100°  120°  140° 

5 77  111  136  159  179  199  216  234  250  266  296  325 

10 109  156  192  226  254  281  306  330  354  376  418  460 

15 133  192  236  275  312  344  376  405  432  461  513  565 

20 .154  221  273  319  359  398  434  467  500  532  592  650 

25 173  248  305  357  402  445  4S5  522  560  595  660  728 

SO ISO  271  334  390  440  487  530  572  612  652  725  798 

35 204  293  360  423  475  527  574  620  662  705  783  862 

40 218  311  386  452  508  562  612  662  707  753  836  920 

45 231  332  408  478  538  597  650  700  750  800  887  977 

50 244  350  432  503  568  630  685  740  790  843  935  1,030 

60 267  383  473  552  622  690  750  810  865  923  1,023  1,125 

70 289  413  510  596  671  746  810  875  935  995  1,1051,215 

80 308  443  545  638  717  705  867  935  1,000  1,065  1.182  1,300 

90 :?27  470  578  678  762  845  920  990  1,060  1,130  1,252  1,380 

100 345  495  610  713  802  890  970  1,045  1,118  1,190  1,323  1,455 

*  Reprinted  from  "  Furnace  Heating."  by  same  author. 


Heat  Given  Off  by  Direct  Radiators  and  Coils. 


52  Principles    of    Heating. 

More  radiation  must  be  used,  however,  since  the  chimney 
effect  of  the  flue  is  decreased  the  nearer  the  top  the  aspirating 
heater  is  placed. 

Where  small  volumes  of  air  are  to  be  removed  coils  or  lines 
of  pipes  may  be  used  to  advantage  in  place  of  cast  iron  radiators, 
care  being  taken  not  to  block  off  too  much  of  the  flue  area.  Such 
coils  may  be  computed  on  a  basis  of  600  heat  units  or  more  per 
square  foot  per  hour,  depending  on  the  flue  velocity. 


CHAPTER  VII. 

THE  LOSS  OF    HEAT   BY  TRANSMISSION,  COMPUTING 
RADIATION,  HORSE  POWER  REQUIRED. 

The  following  tables  have  been  computed  from,  data  presented 
in  a  series  of  articles  on  "  German  Formulas  and  Tables  for  Heat- 
ing and  Ventilating  Work,"  by  Prof.  J.  H.  Kinealy,  beginning 
in  The  Metal  Worker  of  June  18,  1898.  The  values  given  include 
those  for  a  greater  variety  of  building  materials  than  the  writer 
has  seen  published  elsewhere.  The  values  for  glass  and  brick 
work  agree  pretty  closely  with  those  commonly  used  in  this 
country. 

TABLE  X. 

LOSS  OP  HEAT  THROUGH  BRICK   WALLS  OF  APPROXIMATELY  THE   THICKNESS    STATED. 

70  degrees  inside,  0  degree  outside. 

Thickness  of  wall,  inches 8  12          16          20          24          30         36 

Heat  units  per  square  foot  per  hour.  .24          21          18          16          14          12          10 

Tables  showing  the  relative  transmitting  power  of  solid  brick 
walls  and  those  with  air  spaces  about  2.4  inches  wide  show  that 
those  with  the  air  space  transmit  about  15  to  20  per  cent,  less  heat 
than  the  solid  walls.  This  applies  only  to  walls,  say,  8  to  16  inches 
thick.  With  thicker  walls  the  saving  due  to  an  air  space  is  much 
less. 

TABLE  XI. 

LOSS    OF   HEAT   THROUGH    STONE    WALLS,    RUBBLE    OR   BLOCK    MASONRY. 

70  degrees  inside,  0  degree  outside. 

Thickness  of  wall,  inches 12          16          20         24          28          36          44 

Heat  units  per  square  foot  per  hour.  .31          27          25         21          19          17          14 

The  values  given  are  for  sandstone :  about  10  per  cent,  should 
be  added  for  limestone. 

TABLE  XII. 


LOSS    OF    HEAT    THROUGH    PINE    PLANKS. 

70  degrees  inside,  0  degree    outside. 

Thickness  of  planking,  inches 1%         2         2%         3 

Heat  units  per  square  foot  per  hour 21         18         16         14 

S3 


54  Principles    of    Heating. 

TABLE   XIII. 

LOSS  OF  HEAT  THROUGH  WINDOWS  AND  SKYLIGHTS  AND  THROUGH  OUTSIDE  WALLS 
OF  FRAME  CONSTRUCTION,  EXPRESSED  IN  HEAT  UNITS  PER  SQUARE  FOOT  OF 
EXPOSED  WALL  PER  HOUR. 

70  degrees  inside,  0  degree  outside. 

Heat  units 

per 

square  foot 
per  hour. 

Single    window 77 

Single  window,  double  glass 43 

Double   window 32 

Single  skylight 81 

%-inch  sheathing  and  clapboards 20 

%-inch  sheathing,  paper  and  clapboards 16 

Professor  Kinealy  states :  "  These  can  hardly  be  considered 
much  more  than  rough  approximations  on  account  of  the  uncer- 
tainty due  to  leakage." 

TABLE  XIV. 

LOSS  OF  HEAT,  EXPRESSED  IN  HEAT  UNITS  PER  SQUARE  FOOT  OF  SURFACE  PER 
HOUR,  THROUGH  PARTITIONS,  FLOORS  AND  CEILINGS  SEPARATING  WARM  ROOMS 
AT  70  DEGRPJES  FROM  COLO  ROOMS  AT  40  DEGREES. 

Heat  units. 

Ordinary  stud  partition,  lath  and  plaster  one  side  only 18 

Ordinary  stud  partition,  lath  and  plaster  both  sides 10 

Ordinary   lath  and   plaster   ceiling  separating  unheated   space   from    heated 

rooms   18 

Floor,  single,  thickness  %  inch,  warm  air  above  and  cold  space  below  : 

(a)   No  plaster  beneath  joists 13 

(1)   Lath  and  plaster  beneath  joists. 8 

Floor,  double,  thickness  1%  inches,  warm  room  above  and  cold  space  below  : 

(a)   No  plaster  beneath  joists 9 

(&)   Lath  and  plaster  beneath  joists 5 

The  heat  losses  stated  in  the  tables  are  to  be  increased  as  fol- 
lows, based  on  the  practice  of  different  German  engineers: 

TABLE  XV. 

Per  cent. 

For  northeastern,  northwestern,  western  or  northern  exposure 20  to  30 

For  rooms  13  to  14%  feet  high 6Va 

For  rooms  14%  to  18  feet  high 10 

When  the  heating  is  continued  during  the  day  only 10 

When  the  building  is  allowed  to  become  thoroughly  chilled  at  night 30 

When  the  building  remains  for  long  periods  without  heat 50 


COMPUTATION   OF   HEAT   LOSSES   AND  RADIATION. 

To  illustrate  the  use  of  the  German  values  given,  suppose  it 
is  desired  to  compute  the  amount  of  steam  radiation  required  to 


ff  OF  THI 

UNIVERSITY 

OF 

j 

Loss  of  Heat  by  Transmission.  55 

heat  a  corner  room  14.  x  16  x  10  feet,  exposed  to  the  north  and 
west,  located  below  a  heated  room  and  over  an  unheated  room ; 
floor  to  be  double,  with  under  side  of  floor  joists  lathed  and  plas- 
tered; outside  walls  12  inches,  brick;  glass  20  per  cent,  of  the 
exposure,  equal  to  60  square  feet,  net  wall  equaling  240  square 
feet : 

Heat  losses  : 

Wall,  240  X  21  heat  units 5,040 

Glass,  60  X  77  heat  units 4,620 


Total 9,660 

Heat  loss  X  exposure  factor  =  9,660  X  1.25 12^075 

Heat  loss  through  floor,  224  X  5. 1,120 


Total  heat  loss 13,190 

Direct  radiating  surface  is  equal  to  the  total  heat  loss  divided 
by  heat  given  off  per  square  foot  of  radiating  surface — viz. :  250 
heat  units,  or  13,190  -j-  250  =  53  square  feet,  giving  a  ratio  of 
about  i  square  foot  to  43  cubic  feet  of  space.  It  will  be  noted 
that  no  allowance  has  been  made  in  the  above  example  for  air 
leakage.  Professor  Kinealy  points  out  that  the  German  engineers 
appear  to  make  no  allowance  for  this  item,  except  as  taken  into 
account  by  the  percentage  addition  for  exposure.  Some  engi- 
neers in  this  country  allow  for  the  accidental  leakage  by  assuming 
a  certain  rate  of  air  change,  say  once  an  hour,  for  all  rooms. 

In  large  rooms  having  little  exposure  in  proportion  to  the 
contents  the  loss  of  heat  due  to  leakage,  based  on  an  hourly  rate, 
is  often  as  great  as  that  through  the  walls,  if  not  greater,  which 
would  call  for  more  radiation  than  is  found  necessary  in  practice. 

The  question  of  leakage  is  an  important  one  and  requires  good 
judgment  for  its  proper  determination.  In  preference  to  making 
a  fixed  allowance  for  leakage,  based  on  the  cubic  contents,  the 
writer  has  found  it  more  satisfactory  to  consider  the  leakage  to 
be  sufficiently  allowed  for  by  the  exposure  factors  of  1.25  for 
north  or  west  and  1.15  for  east,  especially  when  using  factor  77 
or  85  for  glass,  and  to  make  a  separate  allowance  for  the  effect 
of  the  cubic  contents  on  the  heating  of  a  room  by  adding  to  the 
loss  of  heat  by  transmission  an  amount  of  heat  equal  to  the  cubic 
contents  in  feet  multiplied  by  1-3  for  room  with  two  exposures, 
and  the  cubic  contents  multiplied  by  2-3  for  rooms  with  one 
exposure.  This  allowance  will  be  found  sufficient  to  provide  for 


56  Principles    of   Heating. 

reheating  where  the  rooms  are  allowed  to  become  somewhat 
chilled  at  night. 

The  reason  for  making  a  greater  allowance  for  reheating  in 
the  case  of  rooms  with  one  exposure  than  of  those  with  two  ex- 
posed walls  is  that  the  rate  of  transmission  is  somewhat  greater 
per  square  foot  through  the  single  exposed  wall  having  three 
partition  walls  radiating  heat  to  it  than  through  the  same  wall 
area  of  a  corner  room  having  only  two  interior  walls  radiating 
heat  to  the  outer  ones. 

Furthermore  the  three  inside  walls  on  account  of  their  greater 
surface,  require  more  heat  to  warm  them  in  a  given  time  than 
do  the  two  inside  walls  of  a  corner  room  of  the  same  size,  there- 
fore, in  order  that  corner  rooms  and  single  exposure  rooms  shall 
heat  in  approximately  the  same  time,  a  greater  allowance  for 
reheating  should  be  made  for  the  latter. 

COMPUTING  DIRECT  RADIATION  ON  THE  HEAT  UNIT  BASIS. 

Perhaps  the  most  time  consuming  operation  in  connection  with 
the  work  of  the  heating  engineer  or  contractor  is  the  computation 
of  radiating  surface.  Innumerable  rules  have  been  devised,  good, 
bad  and  indifferent,  but  the  subject  appears  to  have  simmered 
down  to  the  simple  proposition  that  if  the  wall  and  glass  surface 
and  the  required  air  change  are  known  the  heat  losses  due  to 
transmission  and  leakage  may  be  readily  determined,  and  this  total 
divided  by  the  heat  given  off  per  hour  per  square  foot  of  radiating 
surface  gives  the  amount  of  radiation  required. 

The  German  values  for  the  heat  transmitting  power  of  various 
substances  of  different  thicknesses  have  been  widely  used  since 
they  were  first  introduced  by  A.  R.  Wolff.  Tables  or  charts 
giving  these  values  may  be  found  in  Kent's  "  Mechanical  Engi- 
neers' Pocket  Book "  and  in  many  trade  catalogues.  Values 
closely  approximating  these  have  been  stated.  The  French  values, 
based  on  the  investigations  of  Peclet  and  introduced  by  Profes- 
sor Carpenter,  are  in  some  cases  considerably  lower  than  those 
just  mentioned,  his  value  or  coefficient  for  glass  being  70,  Wolff's 
being  85.  Furthermore,  Carpenter  assumes  a  certain  air  change 
per  hour  by  leakage  in  rooms  heated  by  direct  radiation,  whereas 
Wolff  provides  for  this  loss  by  adding  a  certain  percentage  to 


Loss  of  Heat  by  Transmission. 


57 


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CHART   I. 

Ratios  for  DIRECT  STEAM  Radiating  Surface  in  Rooms  with  TWO  SIDES 
EXPOSED  Toward  the  North  and  West,  with  Glass  Surface  Aggregating  20 
Per  Cent,  of  Total  Exposure. 

For  northeast  corner  rooms  use  ratio  5  per  cent,  greater  than  given  by  chart. 

For  southwest  corner  rooms  use  ratio  10  per  cent,  greater  than  given  by  chart. 

For  southeast  corner  rooms  use  ratio  15  per  cent,  greater  than  given  by  chart. 


58  Principles    of    Heating. 

the  heat  losses  through  walls  and  glass.  Of  course,  where  the 
leakage  is  great,  as  in  rooms  provided  with  ventilating  flues,  it  is 
allowed  for  independently. 

Admitting  that  the  wall  and  glass  surface  affords  the  best 
basis  on  which  to  compute  the  radiating  surface,  it  frequently 
happens  in  a  contractor's  office  that  insufficient  time  is  given  in 
which  to  lay  out  the  work  on  this  basis  and  prepare  a  bid.  In. 
house  heating  work  especially  some  shorter  method  must  often 
be  used  for  the  reason  stated.  In  such  cases  an  experienced  man. 
may  be  able  to  hit  pretty  close  to  the  mark  by  "  thumb  rule/'  butr 
while  quick,  this  method  is  a  rather  rough  one. 

Some  simple  method  that  will  give  reasonably  accurate  results 
that  may  be  quickly  arrived  at  is  needed  by  many  contractors. 
The  author  prepared,  and  has  for  several  years  used,  the  accom- 
panying charts,  Nos.  i  and  2,  for  computing  direct  steam  and  3. 
and  4  for  direct  hot  water  radiation,  the  curves  representing  the 
mean  or  average  of  the  German  and  French  values  with  these 
modifications : 

To  the  heat  loss  through  walls  and  glass,  based  on  German 
values,  has  been  added  a  certain  amount  to  allow  for  reheating; 
the  air  in  the  rooms  in  case  they  should  become  chilled. 

To  the  heat  losses  by  transmission,  computed  on  the  French 
basis,  has  been  added  an  amount  representing  the  heat  units  es- 
caping by  a  leakage  of  air  equal  to  the  contents  of  the  room  once 
each  hour. 

The  tables  are  based  on  a  glass  surface  equal  to  20  per  cent, 
of  the  total  exposure.  This  the  author  has  found  to  be  a  fair 
allowance ;  some  rooms  may  have  more  than  this  amount,  but  an 
excessive  glass  surface  is  readily  detected  in  inspecting  plans  and 
may  be  allowed  for  by  adding  to  the  radiating  surface  given  by 
the 'chart  an  amount  of  radiation  equal  to  about  one-third  of  the 
excess  of  glass  surface  over  the  20  per  cent,  on  which  the  charts 
are  based. 

For  example :  If  the  total  exposure  is  400  square  feet  and  the 
glass  surface  120  square  feet,  or  40  square  feet  in  excess  of  the 
glass  surface  based  on  20  per  cent,  of  the  exposure,  13  square 
feet,  being  one-third  of  40,  should  be  added  to  the  radiation  com- 
puted by  the  chart. 


Loss  of  Heat  by  Transmission. 

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CHART  2. 

Ratios   for   DIRECT   STEAM   Radiating   Surface   in    Rooms    Having   Only    ONE 

SIDE  EXPOSED  Toward  North  or  West,  with  Glass  Surface  Aggregating  20 

Per  Cent,  of  Total  Exposure. 

Curve  1  is  for  rooms  having  length  to  width  as  2  to  1,  with  short  side  exposed. 
Curve  3  is  for  rooms  having  length  to  w'dth  as  2  to  1,  with  long  side  exposed.. 
Curve  2  is  for  square  rooms  with  one  side  exposed. 
For  rooms  with  east,  south  or  southeast  exposure  use  ratio  10  per  cent,  greater 

than  chart. 
For  rooms  with  southwest  or  northeast  exposure  use  ratio  5  per  cent,  greater 

than  chart. 


60  Principles    of    Heating. 

Chart  No.  I  shows  a  curve  from  which  the  proper  ratios  of 
steam  heating  surface  to  cubic  contents  may  be  determined  for 
rooms  with  two  exposed  sides.  The  curve  was  computed  for 
square  rooms.  Rectangular  rooms  of  good  proportions,  however, 
have  but  little  more  exposed  wall  surface  in  proportion  to  their 
contents,  and  unless  they  are  unusually  long  and  narrow  the  ratio 
given  by  the  chart  may  be  safely  used.  The  contents  expressed 
in  thousands  of  cubic  feet  is  stated  on  the  lower  line  and  the 
ratio  of  radiating  surface  to  contents  is  given  in  the  vertical  line 
at  the  left  of  the  chart. 

Example:  What  radiating  surface  should  be  used  in  a  corner 
room  16  x  19  x  10  feet,  having  3040  cubic  feet?  Just  to  the 
right  of  the  3000  line  is  a  point  representing  the  contents  of  3040 
cubic  feet.  Note  where  a  line  drawn  vertically  through  this  point 
would  intersect  the  curve.  In  the  left  hand  column  this  point  of 
intersection  is  the  ratio  sought.  The  ratio  in  this  case  is  about 
i  to  47.  The  contents  (3040)  divided  by  this  ratio  gives  63 
square  feet  of  direct  radiating  surface. 

Chart  No.  2,  for  rooms  with  one  exposure,  contains  three 
curves, 'one  for  rooms  with  sides  in  the  proportion  of  2  to  I  (24 
x  12  feet,  for  example),  having  the  long  side  exposed;  one  for 
similar  rooms  with  the  short  side  exposed  and  one  for  square 
rooms.  Obviously  it  makes  a  great  difference  whether  the  long 
or  the  short  side  of  a  room  is  exposed. 

For  rooms  having  sides  in  the  proportion  of  1^2  to  I  (15  x 
10  feet,  for  example),  with  the  long  side  exposed,  compute  the 
contents  and  proceed  as  explained  in  connection  with  Chart  No. 
i,  selecting  a  point  in  Chart  2  midway  between  curve  2  and  curve 
3  on  the  vertical  line  corresponding  with  the  contents.  The 
proper  ratio  will  be  found  in  the  left  hand  column  opposite  this 
midway  point. 

With  rooms  like  the  one  described,  but  having  the  short  side 
exposed,  select  a  point  midway  between  curve  I  and  2. 

Example :  What  amount  of  steam  radiating  surface  is  required 
in  a  room  12  x  18  x  10  feet,  having  the  12-foot  wall  exposed? 
Contents  2160  cubic  feet.  On  Chart  2  follow  up  the  line  represent- 
ing the  contents  to  a  point  midway  between  curves  i  and  2,  then 
out  horizontallv  to  the  left  hand  column.  The  ratio  there  found  is 


Loss  of  Heat  by  Transmission. 


61 


RATIOS  1    TO 

§  8 


I- 

8 


CHART  3. 

Ratios  for  DIRECT  HOT  WATER  Radiating  Surface,  Open  Tank  System,  in 
Rooms  with  TWO  SIDES  EXPOSED  Toward  the  North  and  West,  with 
Glass  Surface  Aggregating  20  Per  Cent,  of  Total  Exposure. 

For  northeast  corner  rooms  use  ratio  50  per  cent,  greater  than  chart. 

For  southwest  corner  rooms  use  ratio  10  per  cent,    greater  than  chart. 

For  southeast  corner  rooms  use  ratio  15  per  cent,  greater  than  chart. 


62 


Principles   of   Heating. 


RATIOS  1  TO 


CHART  4. 

Ratios  for  DIRECT  HOT  WATER  Heating  Surface,  Open  Tank  System,  in  Rooms 
with  Only  ONE  SIDE  EXPOSED  Toward  the  North  or  West,  with  Glass 
Surface  Aggregating  20  Per  Cent,  of  the  Total  Exposure. 

Curve  1  is  for  rooms  having  length  to  width  as  2  to  1,  with  short  side  exposed. 

Curve  3  is  for  rooms  having  length  to  width  as  2  to  1,  with  long  side  exposed. 

Curve  2  is  for  square  rooms,  with  one  side  exposed. 

For  rooms  with  east,  south  or  southeast  exposure  use  ratio  10  per  cent,  greater 
than  chart. 

For  rooms  with  southwest  or  northeast  exposure  use  ratio  5  per  cent,  greater 
than  chart. 


Loss  of  Heat  by  Transmission.  63 

about  i  to  72,  and  the  radiating  surface  2160  -^  72  —  30  square 
feet. 

With  this  explanation  of  charts  No.  I  and  No.  2  for  steam 
heating,  the  use  of  charts  No.  3  and  No.  4  for  hot  water  heating 
will  be  readily  understood  without  further  examples. 

THE    BOILER   HORSE-POWER   AND    RADIATING   SURFACE   REQUIRED   TO 
HEAT    ISOLATED   BUILDINGS. 

It  is  of  interest  to  compute  on  a  heat  unit  basis  the  boiler 
horse-power  necessary  to  heat  buildings  under  the  conditions 
stated  in  connection  with  Chart  6. 


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CUBIC  CONTENTS 

Chart   5. — Space   Heated   Per  Boiler  Horse-Power   in   Isolated   Buildings   Under 

Conditions  Stated. 

Chart  No.  5  shows  by  the  curve  the  increased  space  that  may- 
be warmed  per  boiler  horse-power  in  large  buildings  over  that 
in  smaller  ones,  since  the  former  have  less  exposed  surface  per 
unit  of  contents. 

Chart  No.  6  is  based  on  buildings  ranging  in  size  from  100,- 
ooo  to  1,000,000  cubic  feet  and  in  hight  from  20  to  about  60  feet, 


64  Principles    of   Heating. 

according  to  the  size.  The  buildings  are  assumed  to  be  rectan- 
gular in  plan,  the  length  being  twice  the  breadth  in  each  case. 
The  glass  surface  is  assumed  to  be  one-third  of  the  total  expo- 
sure; the  equivalent  glass  surface  of  the  roof  is  taken  as  one- 
tenth  the  total  area  of  same.  An  allowance  for  reheating  the 
buildings  was  made  equivalent  to  an  amount  of  heat  that  would 
raise  a  volume  of  air  equal  to  the  contents  20  degrees  in  one  hour, 
This  amount  of  heat  would  not  actually  raise  the  temperature 
of  the  air  in  the  building  that  amount  in  the  time  stated,  since 
the  walls  and  machines  or  what  not  in  the  rooms  must  have  their 
temperature  raised  as  well  as  that  of  the  air,  and  would  absorb 
a  large  portion  of  the  heat.  The  greater  the  amount  of  material 
in  the  rooms  the  less  will  be  the  fluctuation  in  temperature  with 
intermittent  heating,  since  the  machinery  or  goods  that  become 
thoroughly  warmed  during  the  day,  when  surrounded  by  air  at, 
say,  60  to  70  degrees  temperature,  store  up  heat  which  is  given 
off  during  the  night  or  at  times  when  steam  is  shut  off. 

For  direct  radiating  systems  the  charts  will  be  of  service  in 
checking  roughly  the  boiler  horse-power  required.  They  apply 
only  to  buildings  exposed  on  all  sides  under  the  conditions  stated 
as  to  glass  surface,  exposure,  etc.  For  other  conditions  due  allow- 
ances must  be  made. 

On  the  basis  of,  say,  85  square  feet  of  radiating  surface  per 
boiler  horse-power,  mains  and  risers  to  be  computed  as  radiating 
surface  unless  covered,  the  horse-power  indicated  in  Chart  No. 
6,  multiplied  by  85,  gives  roughly  the  square  feet  of  radiating 
surface  necessary  for  buildings  of  contents  stated.  For  exam- 
ple: A  building  of  200,000  cubic  feet  requires  20  horse-power, 
per  chart  No.  6  =  20  X  85  =  1700  square  feet  of  radiating  sur- 
face, a  ratio  of  approximately  I  to  120  cubic  feet.  For  400,000 
cubic  feet,  radiating  surface  =  about  33  X  85  =  2805,  giving 
a  ratio  of  I  to  143  cubic  feet,  and  so  on. 

Of  course,  the  above  is  to  be  considered  as  only  a  rough  ap- 
proximation. The  figure  85  is  perhaps  too  conservative.  For  ac- 
curate work  the  wall  and  glass  surface  must  be  computed. 

SIZE  OF  HEATERS   WITH   BLOWER  SYSTEMS. 

With  the  blower  system  the  inleakage  of  cold  air  will  be  some- 
what diminished  by  the  pressure  in  the  rooms  maintained  by  the 


Loss  of  Heat  by  Transmission. 


so 


, 

Sa 


66  Principles    of    Heating. 

fan.  This  pressure  is  scarcely  measurable,  however,  and  its  effect 
in  preventing  inleakage  of  coJd  air  will  be  neglected  in  this  dis- 
cussion. With  air  supply  at  140  degrees  and  building  at  70  de- 
grees, half  the  heat  supplied  is  carried  away  by  the  air  escaping 
at  70  degrees,  the  other  half  being  lost  by  transmission  through 
walls,  windows  and  roof.  Under  these  conditions  twice  as  much 
heat  is  necessary  as  with  direct  radiation. 

If  the  frequent  change  of  air  incident  to  the  blower  system 
is  necessary,  or  if  ample  exhaust  steam  is  available,  well  and 


CUBIC  CONTENTS 

CHART   6. 
Showing  Boiler  Horse-Power  for  Isolated  Building  Under  Conditions  Stated. 

good ;  otherwise  the  loss  of  heat  over  direct  radiation  is  a  serious 
one. 

Since  a  building  with  the  blower  system,  under  the  conditions 
stated,  taking  air  from  the  outside,  will  require  twice  as  much  heat 
as  with  direct  radiation,  the  boiler  horse-power  shown  in  Chart 
No.  3  must  be  doubled ;  for  example,  a  building  of  200,000  cubic 
feet  will  require  about  2  X  20  —  40  horse-power,  and  on  the  basis 
of  50  lineal  feet  of  i-inch  pipe  in  the  heater  per  horse-power,  a 


Loss  of  Heat  by  Transmission.  67 

not  uncommon   allowance,   a  2000  lineal   foot  heater  would  be 
required. 

With  other  conditions  than  140  degrees,  70  degrees  and  zero,, 
as  stated  above,  greater  or  less  boiler  horse-power  would  be  re- 
quired with  lower  or  higher  inlet  temperatures,  respectively.  A 
much  higher  inlet  temperature  than  140  degrees  is  not  to  be 
generally  recommended.  With  the  blower  system  the  heater 
pipes,  with  low  pressure  steam  and  ordinary  velocities  of  air 
between  them,  are  generally  rated  to  give  out  2000  heat  units  or 
more  per  square  foot  an  hour,  or,  say  an  average  of  600  heat  units 
per  lineal  foot  of  i-inch  pipe,  corresponding  to  55  lineal  feet  per 
horse-power. 

RELATIVE     LOSS     OF     HEAT     FROM     BUILDINGS     HAVING     THE     SAME 
CUBIC  CONTENTS. 

The  relative  loss  of  heat  from  buildings  having  the  same  con- 
tents,  but  of  different  forms,  is  shown  in  the  diagrams  ABC  and 
D  of  Fig.  26  A,  each  of  approximately  125,000  cubic  feet.  Let  each 
have  glass  equal  to  one-sixth  the  exposure,  the  equivalent  glass 
surface  of  walls  to  equal  the  area  of  wall  surface  divided  by  4,  and 
let  i  square  foot  of  roof  be  considered  equivalent  to  one-tenth 
square  foot  of  glass;  the  equivalent  glass  surface  of  each  build- 
ing is  as  stated  under  the  different  figures.  Since  the  cubic  con- 
tents is  the  same,  the  loss  of  heat  would  be  roughly  propor- 
tional to  the  equivalent  glass  surface  in  each.  Long,  low  build- 
ings require  less  horse-power  per  looo  cubic  feet  than  those  more 
nearly  cubical  in  form. 

Building  D,  which  is  high  in  proportion  to  its  floor  area,  would 
take  considerably  more  horse-power  per  1000  cubic  feet  than 
those  represented  by  A,  B  or  C. 

The  loss  of  heat  by  leakage  of  air  would  be  greater  in  high 
buildings  like  D  than  in  low  ones  like  B  and  C,  as  they  have  a 
greater  flue  action  involving  greater  leakage  and  have  more  wall 
surface  in  proportion  to  their  contents  than  those  shown  in  A, 
B  and  C. 


CHAPTER    VIII. 
HEATING  WATER. 

The  question  frequently  comes  up  how  to  determine  the  heat- 
ing surface  required  to  heat  a  given  volume  of  water  a  certain 
number  of  degrees  in  hot  water  storage  tanks  or  generators, 
as  shown  in  Fig.  27.  The  proportions  of  feed  water  heaters  in 
connection  with  boilers  give  a  basis  for  such  calculations,  these 
heaters  of  the  closed  tubular  type  having  1-3  to  y2  square  foot 
of  heating  surface  per  boiler  horse-power. 

HEATING    WATER    BY    SUBMERGED    STEAM    PIPES. 

Taking  the  greater  amount  as  a  basis,  J^  square  foot  of  heat- 
ing surface  is  expected  to  heat  about  30  pounds  of  water  per  hour 
from,  say,  50  to  200  degrees,  that  is  30  X  150  =  4500  heat  units. 
In  other  words,  a  square  foot  is  rated  to  transmit  9000  heat  units 
per  hour. 

Suppose  the  exhaust  steam  pressure  is  2  pounds,  correspond- 
ing to  a  temperature  of  about  220  degrees,  the  average  water 
temperature  is  (200  +  50)  -r-  2  =.  125  degrees,  making  the  aver- 
age difference  in  temperature  between  the  steam  and  the  water 
220  —  125  =  95  degrees.  Hence  the  number  of  heat  units  trans- 
mitted per  square  foot  of  heating  surface  per  hour  per  degree 
difference  in  temperature  is  9000  -4-  95,  or  about  100  heat  units 
in  round  numbers. 

Low  pressure  steam  coils  surrounded  by  air  at  70  degrees 
give  off  only  about  2  heat  units  per  degree  difference  in  temper- 
ature per  hour,  whereas  when  immersed  in  -water  they  condense 
steam  per  degree  difference  about  50  times  as  rapidly— a  strik- 
ing fact. 

To  take  a  practical  example,  suppose  it  is  desired  to  compute 
the  heating  surface  in  brass  pipe  required  to*  raise  the  tempera- 
ture of  the  water  in  a  4OOO-gallon  tank  from  70  degrees  to  160 
degrees  in  two  and  one-half  hours  with  steam  at  5  pounds  pres- 
sure. The  given  number  of  gallons  is  equivalent  to  4000  X  8  1-3 
(number  of  pounds  per  gallon)  =  33,333  pounds.  The  increase 


Heating    Water.  69 

in  temperature  is  90  degrees.  Total  number  of  heat  units  re- 
quired is  therefore  33,333  X  90  =  2,999,970.  The  number  of 
heat  units  required  per  hour  is  thus  approximately  1,200,000.  The 
average  difference  in  temperature  between  the  steam  and  water 
is  228  —  115  =  113  degrees.  Since  i  square  foot  of  heating  sur- 
face with  i  degree  difference  between  the  temperature  of  the 
steam  and  water  gives  off  approximately  100  heat  units  per  hour, 
with  113  degrees  difference  approximately  11,300  heat  units  will 
be  given  off  in  an  hour,  and  1,200,000  -i-  11,300  =  106  square 


WATER  OUTLET 


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WATER  INtETll 

THE   METAL.  WORKER 


Fig.  27. — Hot  Water  Storage  Tank  Heated  by  Steam. 

feet,  the  area  of  the  heating  surface  required,  which  is  i  square 
foot  to  approximately  37  gallons  capacity. 

HOT   WATER    GENERATORS. 

Hot  water  generators,  so-called,  otherwise  known  as  coil  boil- 
ers or  hot  water  storage  tanks,  commonly  have  about  i  linear 
foot  of  i -inch  pipe  to  each  5  gallons  capacity — that  is,  about  I 
square  foot  of  heating  surface  to  each  15  gallons  capacity.  Such 
boilers  are  commonly  assumed  to  be  capable  of  heating  their  con- 
tents at  least  once  an  hour  from,  say,  60  to  1 60  degrees. 

To  heat  300  gallons  per  hour,  for  example,  100  degrees  would 
require  the  expenditure  of  300  X  8  1-3  X  100  =  250,000  heat 
units  (8  1-3  representing  the  approximate  weight  of  i  gallon  of 
water  in  pounds).  With  a  coil  based  on  the  proportions  stated, 
i  square  foot  to  15  gallons  capacity,  the  heating  surface  is  20 
square  feet  and  the  heat  emitted  per  square  foot  per  hour  would 
be  250,000  -i-  20  —  12,500  heat  units. 

With  steam  at  228  degrees  and  average  water  temperature  at 


70  Principles    of    Heating. 

no  degrees  the  difference  is  118  degrees;  the  transmission  per 
square  foot  per  hour  per  degree  difference  is  12,500  -f-  118  = 
106  heat  units. 

A  hot  water  generator  of  even  moderate  size  when  heating 
the  contents  once  an  hour  condenses  an  immense  amount  of  steam. 
Take,  for  example,  one  of,  say.  300  gallons  capacity.  To  heat  this 
volume  from,  say,  50  to  160  degrees  requires  300  X  8  1-3  X  no 
—  275,000  heat  units.  The  condensation  of  i  pound  of  steam  at  5 
pounds  pressure  gives  off  954.6  heat  units ;  therefore  nearly  300 
pounds  of  steam  would  have  to  be  condensed  in  an  hour,  equiva- 
lent to  about  10  boiler  horse-power,  or  the  consumption  of  35 
to  40  pounds  of  coal. 

In  office  buildings  and  apartment  houses  at  certain  periods 
theJ  volume  of  water  drawn  from  the  hot  water  generator  is  equal 
to  a  per  hour  rate  many  times  in  excess  of  the  average  per  hour 
requirements  throughout  the  day.  The  generator,  or  hot  water 
storage  tank,  must  be  made  large  enough  to  meet  these  demands, 
just  as  a  storage  battery  is  used  to  carry  an  electric  plant  through 
certain  periods  of  overload.  The  steam  coil  in  the  generator  then 
has  several  hours  in  which  to  make  good  the  sudden  large  drafts 
that  occur  at  intervals. 

BOILING   LIQUIDS    IN   VATS. 

It  is  a  well-known  fact  that  when  water  is  heated  in  an  open 
vessel  to  the  boiling  point,  212  degrees  F.,  its  temperature  cannot 
be  increased.  If  more  heat  is  applied  it  simply  causes  the  water 
to  boil  more  rapidly.  The  amount  of  heat  required  to  evaporate 
i  pound  of  water  at  a  temperature  of  212  degrees  into  steam  at 
the  same  temperature  is,  neglecting  decimals,  966  heat  units.  This 
is  known  as  the  latent  heat.  The  same  number  of  heat  units  are 
given  up  by  the  steam  when  it  is  condensed  back  into  water. 
For  example,  an  ordinary  heating  coil  condensing  about  1-3 
pound  of  steam  per  square  foot  per  hour  gives  off  a  little  more 
than  300  heat  units,  or  about  one-third  of  the  latent  heat  in  a 
pound  of  steam. 

In  computing  the  amount  of  coil  necessary  to  evaporate  a 
given  amount  of  water  in  a  stated  time  proper  allowance  must 
be  made  for  the  latent  heat  necessary  to  evaporate  the  water  after 


Heating    Water.  71 

sufficient  heat  has  been  applied  to  bring  it  to  the  boiling  point. 
Since  the  heat  given  off  by  the  coil  depends  on  the  difference  in 
temperature  between  the  steam  inside  and  the  water  outside  one 
should  have  20  to  40  pounds  steam  pressure  in  order  to  provide 
a  reasonable  excess  of  temperature  in  the  steam  over  the  water. 
For  boiling  thick,  heavy  liquids  considerably  more  heating  sur- 
face is  necessary  than  for  boiling  water,  on  account  of  the  more 
sluggish  circulation.  The  difference  in  the  specific  heats  also 
enters  in. 

HEATING  SMALL  SWIMMING  POOLS. 

Hot  water  generators  fitted  with  steam  coils,  as  shown  in  Fig. 
27,  are  sometimes  used  to  heat  small  swimming  pools,  the  water 
being  admitted  to  the  latter  through  concealed  pipes  placed  near 
the  bottom. 

When  connected  with  a  gravity  return  system  of  steam  heat- 
ing no  more  attention  is  necessary  with  regard  to  maintaining 
the  proper  amount  of  water  in  the  steam  boiler  than  if  the  steam 
coil  in  the  hot  water  generator  were  a  large  radiator,  since  the 
condensation  returns  to  the  boiler,  provided  the  generator  is  lo- 
cated well  above  the  water  line. 

To  compute  the  size  of  coil  required  with  this  method  of 
heating  take,  for  example,  a  pool  12  x  30  feet  in  plan  and  5  feet 
in  average  depth.  Its  contents,  1,800  cubic  feet,  multiplied  by 
623/2,  the  number  of  pounds  i  cubic  foot  of  water  weighs,  gives 
about  112,500  pounds  to  be  heated. 

Suppose  the  water  to  be  continuously  changing  at  the  rate  of 
one  complete  change  every  ten  hours,  equivalent  to  11,250  pounds 
of  water  per  hour.  If  the  water  in  the  street  mains  is  at,  say,  50 
degrees,  and  that  in  'the  pool  75  degrees,  11,250  X  25  =  281,250 
heat  units  must  be  supplied  per  hour.' 

It  has  been  pointed  out  that  I  square  foot  of  heating  surface 
in  the  generator  will  give  out  about  12,500  heat  units  per  hour; 
therefore  281,250  -r-  12,500  =  22.5,  or  about  22  square  feet  of 
coil  would  be  necessary  when  using  steam  of,  say,  5  pounds  pres- 
sure. On  the  customary  basis  of  i  square  foot  of  heating  sur- 
face to  15  gallons  capacity,  22  square  feet  of  surface  would  cor- 
respond to  a  33O-gallon  boiler,  which,  from  experience,  the  writer 
has  found  gives  good  service  under  the  conditions  stated. 


Principles    of     Heating. 


Heating    Water.  73 

HEATING  LARGE  SWIMMING   POOLS. 

For  heating  large  pools  one  of  three  methods  is  commonly 
used: 

1.  Steam  is  admitted  directly  to  the  water  in  the  pool  through 
one  of  the  devices  on  the  market  for  muffling  the  sound. 

2.  Steam  coils  are  submerged  in  the  pool. 

„  3.  The  water  is  made  to  circulate  through  a  boiler  or  heater, 
as  shown  in  Fig.  28,  the  pool  being  practically  a  huge  expansion 
tank. 

AMOUNT  OF  STEAM  AND  SIZE  BOILER  REQUIRED. 

The  amount  of  steam  that  must  be  admitted  to  heat  the  water 
in  a  pool  will  depend  on  the  volume,  the  temperature  and  the 
time  in  which  the  heating  must  be  done. 

Take,  for  example,  a  pool  20  x  80  feet,  with  an  average  depth 
of  7  feet,  equal  to  11,200  cubic  feet,  in  which  the  water  is  to  be 
heated  from  the  street  temperature  of,  say,  50  degrees,  to  a  tem- 
perature of  80  degrees  during  a  period  of  ten  hours.  Water 
at  the  street  temperature  weighs  approximately  62l/2  pounds  per 
cubic  foot;  therefore  11,200  cubic  feet  of  water  to  be  raised  30 
degrees  in  ten  hours  will  require  a  number  of  heat  units  per  hour 
equal  to 

11,200  X  62.5  X  30  -r-  10  =  2,100,000  heat  units. 

Suppose  the  steam  be  admitted  at  low  pressure,  say  5  pounds. 
One  pound  at  that  pressure  will  supply  955  heat  units  when  con- 
•densed,  and  the  water,  in  cooling  from  228  degrees,  the  tempera- 
ture of  the  steam  at  5  pounds  pressure,  to  80  degrees,  will  give 
up  148  heat  units  more,  making  a  total  of  1,103  neat  units  per 
pound.  This  figure  is  contained  in  the  total  number  of  heat  units 
required  about  1,903  times — that  it,  1,903  pounds  of  steam  must 
be  condensed  in  one  hour. 

The  boiler  capacity  required  is  equal  to  2,100,000  -f-  33,305 
(which  is  a  boiler  horse-power  expressed  in  heat  units)  =63 
horse-power.  The  above  makes  no  allowance  for  the  loss  of  heat 
by  evaporation — a  subject  previously  discussed — nor  for  losses 
through  the  walls  or  the  bottom  of  the  tank. 


74  Principles    of   Heating. 

AMOUNT  OF  STEAM    PIPE  REQUIRED. 

To  ascertain  the  amount  of  steam  pipe  required  with  steam  at, 
sav>  5  pounds  pressure,  the  pipes  to  be  placed  around  the  tank 
in  recesses  near  the  bottom,  other  conditions  to  be  as  stated  above, 
proceed  as  follows :  The  average  difference  in  temperature  be- 
tween the  steam  and  water  is 

/  50  +  80  \ 
228  —  { )=  228  —  65  =  163  degrees. 

The  discussion  of  feed  water  heaters  showed  that  it  is  approx- 
imately correct  to  reckon  on  100  heat  units  being  given  off  per 
hour  by  the  steam  to  the  surrounding  water  per  degree  difference 
in  temperature.  Hence,  with  163  degrees  difference,  we  should 
expect  to  transmit  to  the  water  16,300  heat  units  for  each  square 
foot  of  brass  pipe  installed.  If  galvanized  wrought  iron  pipes  are 
used  we  should  expect  to  get  only  about  70  per  cent,  of  the  heat 
stated  above,  or  11,410  heat  units  per  square  foot  per  hour. 

The  total  heat  units — viz.,  2,100,000 — divided  by  11,410,  gives 
184  square  feet,  or  about  368  linear  feet,  of  il/2 -inch  pipe  that 
would  be  required  to  meet  the  conditions  stated.  If  the  water 
were  to  be  heated  in  a  shorter  time  proportionately  more  surface 
would  be  required. 

The  above  computations  have  as  a  basis  the  heat  given  off  by 
the  pipes  or  tubes  in  feed  water  heaters  where  the  circulation  of 
water  is  comparatively  rapid.  With  coils  submerged  in  tanks 
the  movement  of  water  over  them  is  sluggish  and  the  heat  is 
taken  up  from  the  pipes  less  rapidly,  hence  it  is  wise  to  add  25  to 
50  per  cent,  to  the  computed  amount  of  pipe  according  to  its 
location  to  allow  for  this  sluggish  circulation. 

SIZE  BOILER  REQUIRED. 

If  a  boiler  is  to  be  used,  as  in  the  third  method  mentioned,  the 
amount  of  coal  to  be  burned,  the  size  of  the  grate  and  the  size  of 
the  boiler  may  be  determined  as  follows : 

The  total  number  of  heat  units  required  per  hour,  as  computed 
above,  is  2,100,000.  Assuming  that  i  pound  of  coal  will  give  up 
in  this  case  9,000  heat  units,  since  the  boiler  will  be  more  efficient 
than  usual,  due  to  the  cooler  heating  surfaces,  the  coal  required 
will  be  2,100,000  -f-  9,000  =  233  pounds  per  hour.  With  a  regu- 


Heating    Water.  75 

lar  attendant  at  least  an  8-pound  rate  of  combustion  per  square 
foot  of  grate  surface  f>er  hour  may  be  safely  assumed.  The  grate 
surface  therefore  should  be  233  -f-  8  =  approximately  30  square 
feet. 

The  water  in  the  boiler  being  only  80  odd  degrees  instead  of, 
say,  228  degrees,  with  5  pounds  pressure,  less  heating  surface  is 
required,  in  proportion  to  the  grate  area  than  with  ordinary  heat- 
ing boilers  to  give  the  same  efficiency.  Assuming,  as  a  rough  ap- 
proximation, that  the  average  temperature  of  the  gases  in  the 
boiler  or  heater  is  700  degrees,  the  effectiveness  of  the  heating 

surface  in  the  two  cases  would  be  in  the  proportion  of— 

700  —  228 

;  that  is,  only  about  472  -r-  620  =  76  per  cent,  as  much 
472 

heating  surface  per  square  foot  of  grate  would  be  required  in  the 
boiler  used  for  heating  water  to  80  or  90  degrees  as  would  be 
needed  in  ordinary  low  pressure  boilers. 

The  gist  of  this  is  that  a  heater  for  the  purpose  stated  could 
have  an  abnormally  large  grate  in  proportion  to  its  size  and  still 
be  economical  in  the  use  of  coal. 

TANK    HEATERS. 

Tank  heaters  are  commonly  rated  by  manufacturers  to  heat 
one-half  to  three-fourths  as  many  gallons  of  water  per  hour  as 
the  number  of  square  feet  of  direct  radiating  surface  they  will 
supply ;  that  is,  a  heater  with  a  grate  20  x  24  inches  connected  as 
shown  in  Fig.  29,  would  be  rated  to  carry,  say,  600  square  feet  of 
radiating  surface,  or  to  heat  300  to  450  gallons  of  water  per  hour. 
Manufacturers  fail  to  give  the  temperatures  from  and  to  which 
the  water  is  heated,  but  for  apartment  houses  and  the  like  the  tank 
temperature  should  be  kept  as  a  rule  at  about  160  degrees.  There- 
fore the  water  must  be  heated  on  an  average  at  least  100  degrees 
above  that  of  the  city  supply. 

It  is  a  simple  matter  to  show  on  a  heat  unit  basis  that  a  much 
greater  expenditure  of  heat  is  necessary  to  raise  300  gallons — 
that  is,  2,500  pounds — of  water  100  degrees  than  to  supply  600 
square  feet  of  radiating  surface,  the  heat  losses  being  250.000 
and  90,000  respectively.  Therefore  tank  heaters  are  commonly 
overrated.  This  fact,  however,  seldom  becomes  apparent,  as  the 


76  Principles    of    Heating. 

large  capacity  of  the  storage  tank  enables  the  heater  to  heat  the 
water  at  night,  or  when  little  water  is  drawn,  so  that  time  and 
storage  capacity  help  out  the  overrated  heater. 

If  one  knows  approximately  the  number  of  gallons  of  water 
that  must  be  heated  per  hour  to  a  given  temperature  from  that  of 
the  city  supply",  the  size  heater  may  be  readily  determined  on  the 
heat  unit  basis.  For  small  heaters,  having,  say,  not  over  2  square 
feet  grate  surface,  the  rate  of  combustion  should  not  exceed  3 
pounds  per  square  foot  of  grate  per  hour.  Larger  heaters  may 


THE  METAL  WORK.E" 

Fig.  29. — Tank  Heater  Connections. 


be  rated  to  burn  4  to  5  pounds  or  even  more  with  frequent  atten- 
tion. 

Example:  What  size  will  be  required  to  heat  75  gallons  per 
hour  90  degrees?  The  product:  75  (gallons)  X  8  1-3  (number  of 
pounds  of  water  in  one  gallon)  X  90  (the  temperature  range), 
gives  the  number  of  heat  units  involved.  Dividing  this  product 
by  3  (number  of  pounds  of  coal  burned  per  square  foot  of  the 
grate  per  hour)  X  8000  (the  number  of  heat  units  utilized  per 
pound  of  coal)  gives  2.3  as  the  number  of  square  feet  of  grate 
surface  required.  The  above  basis  of  computation  will  be  found 
convenient  in  determining  the  size  heater  to  be  used  for  a  baptistry 
pool,  when  the  volume  to  be  heated,  the  time  and  the  temperature 
to  be  attained  are  known. 


Heating    Water.  77 

By  installing  a  storage  tank  of  good  size  a  small  heater  may 
be  made  to  do  as  good  service  as  a  much  larger  one  with  a  small 
tank.  That  is,  with  a  large  tank,  holding  several  times  the  proba- 
ble maximum  hourly  volume  required,  a  sudden  draft  in  excess 
of  the  ability  of  the  heater  to  make  good  immediately  is  not  ac- 
companied by  a  lowering  of  temperature  at  the  faucets,  as  would 
be  the  case  with  a  small  tank.  The  assumption  is  sometimes 
made  that,  unless  stated  to  the  contrary,  heaters  rated  to  supply 
tanks  of  certain  capacities  are  capable  of  heating  a  volume  of 
water  equal  to  the  tank  capacity  in  one  hour.  As  just  stated,  it 
is  better  that  the  tank  capacity  should  be  several  times  the  average 
hourly  consumption. 

Taking  the  ratings  of  a  prominent  manufacturer: 

Heater  with  12-inch  grate  is  rated  to  supply  a  200-gaIlon  tank. 
Heater  with  15-inch  grate  is  rated  to  supply  a  32.">-gallon  tank. 
Heater  with  18-inch  grate  is  rated  to  supply  a  485-gallon  tank. 

Averaging  these  gives  I  square  foot  of  grate  to  266  gallons 
tank  capacity.  Even  with  a  rapid  rate  of  combustion,  say  5 
pounds  per  square  foot  per  hour,  a  square  foot  of  grate  would  heat 
only  about  48  gallons  per  hour  100  degrees,  showing  the  tank 
capacity  stated  in  these  ratings  to  be  over  five  times  the  hourly 
heating  capacity  of  the  heaters. 

Suppose  the  water  is  heated  from  a  street  main  at  a  tempera- 
ture of  60  degrees  to  only  120  degrees;  then  I  square  foot  of 
grate  with  a  5-pound  rate  of  combustion  would  heat  80  gallons 
per  hour,  or  only  about  one-third  the  rated  tank  capacity  per 
square  foot  stated  in  the  manufacturer's  ratings.  On  the  basis 
of  80  gallons  per  hour  heated  from  60  to  120  degrees  per  square 
foot  of  grate,  a  32O-gallon  boiler,  contents  to  be  used  once  an 
hour,  should  have  a  heater  with  at  least  4  square  feet  of  grate 
surface,  equivalent  to  a  grate  27  inches  in  diameter.  This  would 
be  uncommonly  large  for  a  tank  of  the  size  stated,  showing  that 
with  the  ordinary  proportions  of  grate  to  tank  capacity  it  must 
not  be  expected  that  the  contents  of  the  tank  will  be  heated  in 
less  than  several  hours. 

WATER   BACKS   AND   GAS    HEATERS. 

Water  backs  in  ranges  ordinarily  have  2  to  2^2  square  inches 
of  heating  surface  per  gallon  capacity  in  the  hot  water  boilers 


Principles    of   Heating. 


with  which  they  are  connected.  The  ordinary  temperature  of 
water  from  city  mains  would  be  50  degrees  or  more,  running  up 
to  70  degrees  or  so  in  summer.  While  160  degrees  is  a  common 
temperature  for  the  hot  water  supply  in  large  buildings  having  a 
separate  heater,  the  temperature  of  a  domestic  supply  is  generally 


COLO  WATER 


Fig.  30. — Gas  Heater  Connected  with  Range  Boiler. 

much  lower,  say  not  over  130  degrees  as  a  rule,  though  in  some 
cases  much  higher — even  above  boiling  temperature  at  atmos- 
pheric pressure.  Now,  under  the  most  favorable  conditions  the 
hot  water  supply  must  be  heated  from  70  to  130  degrees,  equal 
to  60  degrees  rise. 

Take,  for  example,  a  4O-gallon  boiler  connected  with  a  water 
back  of  100  square  inches  area.  To  heat  40  gallons  per  hour  60 
degrees  would  take  40  X  8  1-3  X  60  =  20,000  heat  units,  which 


Heating    Water.  79 

with  a  water  back  area  of  about  2-3  square  foot  would  mean  over 
30,000  heat  units  per  square  foot  per  hour  transmitted  to  the 
water.  Such  a  rating  would  be  altogether  too  high  with  the  pro- 
portions of  water  back  and  tank  capacity  just  stated. 

Similar  surfaces  in  furnaces  with  combination  heaters  are  sel- 
dom rated  to  carry  over  75  square  feet  of  direct  radiating  surface 
for  each  square  foot  of  heating  surface  exposed  to  the  fire;  this 
is  equivalent  to  only  75  X  150  (150  being  the  heat  units  given 
off  per  square  foot  of  radiating  surface  per  hour)  ==11,250  heat 
units.  This  is  only  a  little  more  than  the  heat  given  off  per  square 
foot  by  steam  coils  in  contact  with  water.  The  low  rating  is  due 
to  the  chilling  effect  of  the  coil  or  water  back  on  the  fire  in  con- 
tact with  it. 

For  ordinary  working  conditions  the  writer  believes  a  rating 
of  10,000  heat  units  per  square  foot  per  hour  for  water  backs  to 
be  a  fair  one,  but  with  a  brisk  fire,  as  on  ironing  days,  the  water 
back  will  probably  take  up  as  much  as  15,000  heat  units  per 
square  foot  per  hour. 

It  is  pretty  difficult  to  determine  in  advance  in  any  household 
the  approximate  volume  of  hot  water  that  must  be  supplied. 
Families  of  the  same  size  differ  greatly  in  the  amount  of  water 
they  are  in  the  habit  of  using.  A  water  back  to  meet  maximum 
use  would  be  altogether  too  large  for  ordinary  use.  The  best  way 
to  meet  excessive  occasional  demands  is  to  use  a  gas  heater,  con- 
nected as  shown  in  Fig.  30,  in  addition  to  the  water  back. 

Tests  of  ordinary  gas  heaters  used  in  connection  with  hot 
water  boilers  are  stated  to  have  shown  efficiencies  of  52  to  74  per 
cent.,  when  burning  gas  having  a  heating  power  of  540  heat  units 
per  cubic  foot. 

COILS   FOR    HEATING   WATER. 

Coils  for  heating  the  domestic  water  supply  are  frequently 
placed  in  hot  water  or  steam  heaters.  On  the  basis  of  15,000 
heat  units  per  square  foot  per  hour ;  to  heat  40  gallons  per  hour, 
for  example,  from,  say,  60  to  130  degrees,  or  through  70  degrees, 
40  X  S  1-3  X  70  =  23,310  heat  units  would  be  necessary,  re- 
quiring about  il/2  square  feet  of  heating  surface,  equal  to  4^2 
lineal  feet  of  i-inch  pipe  or  3.5  feet  of  i^-inch  pipe. 

If  the  coil  is  suspended  in  the  combustion  chamber  above  the 
fire  a  much  lower  rating  must  be  assumed.  It  is  well  to  arrange 


8o  Principles    of    Heating. 

the  coil  so  that  the  fire  may  be  brought  in  contact  with  it  when 
desired  by  carrying  a  deep  bed  of  coal  on  the  grate.  The  heating 
capacity  of  a  coil  placed  above  the  fire  varies  greatly  with  the 
condition  of  the  fire  on  top ;  a  bright  fire  giving  good  results  and 
one  black  on  top  heating  the  water  but  little.  As  a  rule  it  is  a 
rather  unsatisfactory  way  to  heat  a  water  supply  unless  the  fire  is 
run  very  regularly.  A  good  sized  tank  should  be  used  to  avoid, 
overheating. 

An  independent  hot  water  stove  or  tank  heater  is  generally  to 
be  preferred.  A  rating  as  high  as  15,000  heat  units  should  hardly 
be  used,  except  when  the  fire  is  sure  to  receive  careful  attention. 
A  rating  of  10,000  to  12,000  heat  units  would  represent  more 
closely  what  could  be  expected  in  ordinary  practice. 


CHAPTER  IX. 

THE  FLOW  OF  STEAM  IN  PIPES  AND  THE  CAPACITIES 

OF   PIPES    FOR  STE\M   HEATING  SYSTEMS 

AND  FOR  STEAM  BOILERS. 

The  following  chapter  is  intended  not  as  an  exhaustive  dis- 
cussion of  the  various  methods  of  proportioning  piping  systems, 
nor  of  the  formulas  on  which  the  flow  of  steam  is  based,  but  to 
provide,  by  tables,  a  ready  means  of  solving  problems  relating  to 
pipe  sizes.  The  formulas  on  which  the  tables  are  based  make  due 
allowance  for  the  diminished  resistance  due  to  an  increase  in  the 
size  of  pipes. 

The  cruder,  yet  common,  method  of.  allowing,  for  large  and 
small  pipes  alike,  a  certain  number  of  thousandths  of  a  square 
inch  in  cross  sectional  area  to  each  square  foot  of  radiating  sur- 
face makes  the  larger  pipes  much  greater  in  area  in  proportion  to 
the  surface  supplied  than  the  smaller  ones. 

A  COMPARISON  OF  FORMULAS. 

D'Arcy's  modified  formula,  stated  in  Kent's  "  Mechanical  En- 
gineer's Pocketbook,"  gives  the  weight  of  steam  that  will  flow  per 
minute  through  pipes  of  various  sizes  as 


L (A 

where  w  =  the  density  or  weight  per  cubic  foot  of  steam  at  pres- 
sure pi",  (/>±  —  p2)  =  drop  in  pressure,  or  the  difference  between 
initial  and  terminal  pressure ;  d  =  diameter  of  pipe  in  inches ;  L 
=  length  of  pipe  in  feet ;  c  =  coefficient,  as  follows : 

Diameter  of  pipe  in  inches.   123456789 

Value  of  c 45.3     52.7     56.1     57.8     58.4     59.5     60.1     60.7     61.2 

Diameter  of  pipe  in  inches.  10      11  12         14         16        18        20        22        24 

Value  of  c 61.8     62        62.1     62.3     62.6     62.7     62.9     63.2     63.2- 

Babcock's  formula,  given  in  "  Steam,"  is 


w  =  Srr  — 

I        V        _l_         — I 

.(*) 


SI 


82  Principles    of    Heating. 

This  may  be  reduced  to  a  form  similar  to  D'Arcy's  formula,  but 
with  different  coefficients. 

Table  XVI  has  been  computed  from  these  formulas  in  order 
to  compare  the  results  for  pipes  of  different  sizes.  This  table  is 
based  on  the  actual  inside  diameter  of  standard  wrought  iron 
pipes  of  nominal  sizes  stated  up  to  12  inches,  inclusive.  Sizes 
of  14  inches  and  larger  are  nominal  outside  diameters  of  O.  D. 
pipe,  the  inside  diameter  of  each  being  J^-inch  less  than  the 
outside. 

TABLE    XVI. 

SHOWING  THE  WEIGHT  OF  STEAM  IN  POUNDS  THAT  WILL  FLOW  PER  MINUTE 
THROUGH  STRAIGHT  PIPES  100  FEET  IN  LENGTH  ;  NO  ALLOWANCE  BEING  MADE 
FOR  RESISTANCE  AT  THE  ENTRANCE  TO  THE  PIPE. 

Initial  pressure,  5  pounds  by  gauge,  less  a  drop  in  pressure  in  a  length  of  100 
feet,  1  pound. 

Formula.          , Nominal  diameter  of  pipe  in  inches. x 

1         l',4      !%•       2       2%          3          3%       4        41/3      567 
f — Weight  of  steam,  in  pounds,  flowing  through  pipe  per  minute. — N 

D'Arcy's    1.14     2.38     3.7     G.7     11.6     20.8     30.3     41.4     56     73     118     174 

Babcock's     ....1.05     2.31     3.6     7.3     11.9     21.9     32.7     46.5     63     86     141     208 

Formula.          f Nominal  diameter  of  pipe  in  inches. N 

8          9         10        12  14  16  18  20  22  24 

f — Weight  of  steam,  in  pounds,  flowing  through  pipe  per  minute.— ^ 

D'Arcy's    246     327     438     694         910     1,266     1,735     2,285     2,945     3,660 

Babcock's    293     394     533     853     1,140     1,590     2,210     2,910     3,760     4,730 

APPLICATION  OF  FACTORS  TO  TABLE  XVI. 

Both  formulas  show  the  weight  of  steam  delivered  to  be  pro- 
portionai:  (i)  To  the  square  root  of  the  density  or  the  square 
root  of  the  weight  per  cubic  foot;  (2)  to  the  square  root  of  the 
drop  in  pressure ;  (3)  to  the  square  root  of  the  fifth  power  of  the 
diameter  of  the  pipe,  and  (4)  to  be  inversely  proportional  to  the 
square  root  of  the  length  of  the  pipe. 

For  any  other  pressure  than  5  pounds,  on  which  Table  XVI  is 
based,  mu'tiply  the  figures  there  stated  by  the  square  root  of  the 
density  at  the  given  pressure,  divided  by  the  square  root  of  the 
density  at  5  pounds  pressure.  This  gives  the  following  factors 
for  different  pressures: 

TABLE   XVII. 

FACTORS    TO   BE   APPLIED   TO    TABLE    XVI    FOR   OTHER   GAUGE   PRESSURES   THAN 

5    POUNDS. 

Gauge  pressure  in  pounds 1  2  5  10  15  20  30  40 

Multiplier 0.90  0.93  1.00  1.11  1.21  1.31  1.47  1.61 

Gauge  pressure  in  pounds 50  60  70  80  90  100  110  120 

Multiplier    1.74  1.86  1.97  2.07  2.18  2.26  2.37  2.46 


The    Flow    of   Steam   in   Pipes.  83 

This  table  shows,  for  example,  that  with  50  pounds  pressure 
1.74  times  as  much  steam  by  weight  will  flow  through  a  given  pipe 
as  with  5  pounds  pressure ;  the  drop  in  pressure  being  the  same  in 
each  case. 

For  a  drop  in  pressure  other  than  I  pound,  on  which  Table 
XVL  is  based,  multiply  the  figures  in  that  table  by  the  square  root 
of  the  given  drop  corresponding  to  these  factors. 


TABLE   XVI II. 

FACTORS    APPLY  I XG    TO    TABi.E    XVI    FOR    OTHER    DROPS    IX    PRESSURE    THAN    1    POUND. 


Drop  in  pressure  in  pounds  (pi— #2)     % 
Multiplier    0.354 


0.500     0.709     0.865 


1 

1.00 


2 

1.41 


3 
1.7* 


TABLE   XIX. 

FACTORS  FOR  OTHER  LEXGTHS  THAN  100  FEET.  TOTAL  DROP  IN  PRESSURE 
ASSUMED  TO  BE  1  POUND,  WHATEVER  THE  LENGTH  OF  THE  PIPE  THE  CAPACITY 
OF  WHICH  IS  BEING  COMPUTED.  FACTORS  OR  MULTIPLIERS  TO  BE  USED  IN 
CONNECTION  WITH  TABLE  XVI. 

Length    of    pipe    in 

feet   50      100  150  200  250  300  350  400  -.50 

Multiplier    1.41      1.00  0.816  0.710  0.632  0.578  0.535  0.500  0.471 

Length  of  pipe  in  feet. .    500  550  600  650  700  750  800  850 

Multiplier    0.447  0.427  0.407  0.392  0.379  0.365  0.353  0.343 

Length  of  pipe  in  feet.  .    900  950  1,000  1,200  1,400  1,600  1,800  2,000 

Multiplier    0.333  0.325  0.316  0.288  0.268  0.250  0.236  0.224 

To  illustrate  the  use  of  Tables  XVI,  XVII,  XVIII  and  XIX, 
suppose  it  is  desired  to  compute  the  flow  of  steam  at  50  pounds 
gauge  pressure  through  a  3-inch  pipe  400  feet  long,  the  drop  in 
pressure  to  be  2  pounds.  Table  XVI  gives,  with  D'Arcy's  formula, 
20.8  pounds  as  the  weight  of  steam  passing  in  one  minute  through 
a  pipe  100  feet  long,  with  I  pound  drop  in  pressure.  Applying 
the  factors  in  Tables  XVII,  XIX  and  XVIII,  respectively,  cor- 
responding to  the  above  conditions,  we  have  20.8  X  1.74  X  0.5 
X  1.41  =  25.43  pounds  as  the  weight  of  steam  flowing  through 
the  pipe  per  minute. 

RESISTANCES   TO   THE   FLOW   OF   STEAM. 

In  computing  the  flow  of  steam  from  Table  XVI,  the  resistance 
at  the  entrance  to  the  pipe  at  elbows  and  globe  valves  should  be 
allowed  for  by  adding  to  the  actual  length  of  the  pipe  a  length 
that  would  produce  the  same  resistance  to  the  flow  as  that  at  these 


$4  Principles    of    Heating. 

points.    The  resistance  at  the  entrance  is  commonly  expressed  in 
connection  with  Babcock's  formula  by  the  equation 
_    114  diameters  i(    „ 

-,  +  (3.6  +  d)  • 

where  R  equals  a  length  of  straight  pipe  expressed  in  diameters 
that  would  interpose  the  same  resistance  as  that  at  the  entrance 
.and  d  equals  diameter  of  pipe  in  inches. 

Very  little  has  been  published  giving  the  results  of  tests  bear- 
ing on  this  subject.  Treatises  on  hydraulics,  in  discussing  the 
flow  of  water  in  pipes,  which  follows  the  same  general  laws  as  the 
flow  of  steam,  give  tables  and  data  showing  the  length  of  pipe 
equivalent  in  resistance  to  that  at  entrance  to  be  approximately 
one-third  of  that  given  by  formula  "  c."  The  use  of  formula  "  c  " 
in  computing  pipe  sizes  for  steam  heating  systems  gives  sizes 
much  in  excess  of  those  found  necessary  in  practice.  The  author, 
therefore,  favors  the  use  of 

114  diameters 
R=    I/3  X  i  +  (3.6  -  d) °" 

The  values  corresponding  to  the  latter  formula,  reduced  to 
feet,  are  as  follows : 

TABLE  xx. 

THE  RESISTANCE  AT  THE  ENTRANCE  OF  PIPES  EXPRESSED  IN  THE  NUMBER  OF  FEET 
OF  STRAIGHT  PIPE  THAT  WOULD  PRODUCE  THE  SAME  RESISTANCE  AS  THAT  AT 
THE  ENTRANCE. 

*Nominal                                   Resistance  *Nominal                                 Resistance 

diameter                                     based  on  diameter                                   based  on 

of  pipes                                      Formula  of  pipes                                    Formula 

in  inches.                                  "  d.' — Feet.  in  inches.                                  l>  d." — Feet. 

1 0.8  7 14.7 

114 1.2  8 17.5 

1V2 1.6  9 H0.4 

2 2.4  10 23.4 

21/2 3.1  12 2i).4 

3 4.5  14 U5.3 

31/2 5.1  16 41.3 

4 6.7  18 47.3 

4% 7.9  20 53.6 

5 9.3  22 60.0 

6 12.1  24 ...                                       .  .  G6.0 


*  Nominal  diameter  of  14-inch  pipes  and  larger  is  the  outside  diameter. 

The  resistance  at  a  globe  valve  of  given  size  is  commonly  al- 
lowed for  by  adding  to  the  actual  length  of  pipe  a  length  three 
.times  that  stated  in  Table  XX,  and  for  a  standard  elbow  a  length 
twice  that  stated  in  the  table.  These  values  are,  however,  to  be 


The   Floiv    of    Steam    in    Pipes.  85 

•considered  as  only  approximately  true,  although  they  are  near 
enough  for  practical  use.  The  longer  the  pipe  the  less  will  be 
the  error  in  the  computed  flow  due  to  any  uncertainty  or  error 
in  the  allowance  made  for  the  three  resistances  at  entrance,  elbows 
.and  globe  valves. 

The  use  of  long  turn  elbows  and  straightway  gate  valves 
practically  eliminates  two  of  these  resistance  losses,  and  the  other 
is  considerably  reduced  by  reaming  the  pipes  at  the  ends,  as  is 
common  in  hot  water  work. 

The  following  example  will  illustrate  the  use  of  Table  XVI, 
the  multipliers  in  Tables  XVII,  XVIII,  and  XIX,  and  allowance 
in  Table  XX : 

How  many  pounds  of  steam  will  flow  per  minute  through  a 
4l/2 -inch  pipe  800  feet  long,  with  four  elbows  and  one  globe 
valve?  Initial  gauge  pressure,  10  pounds.  Drop  in  pressure,  2 
pounds. 

Feet. 

Actual   length  of  pipe 800 

Allowance  for  loss  at  entrance  (TableXX  approximately) 8 

Allowance  for  two  elbows 32 

Allowance  for  one  globe  valve 24 

Total  equivalent  length  of  straight  pipe,  making  due  allowances  as  above.    864 

A  length  of  850  feet  is  the  one  most  nearly  corresponding 
to  this  length  in  Table  XIX.  The  factor  for  this  length  is  0.343 ; 
for  10  pounds  pressure  the  factor  in  Table  XVII  is  i.n  ;  for  2 
pounds  drop  in  pressure  the  factor  in  Table  XVIII  is  1.41.  The 
flow  of  steam  in  pounds  by  D'Arcy's  formula,  stated  in  Table  XVI, 
to  which  these  factors  apply,  is  for  a  4^ -inch  pipe  56  pounds. 
For  a  length  of  800  feet,  with  conditions  as  stated,  the  computed 
flow  would  be  56  X  0.343  X  i.n  X  1.41  =  30.1  pounds  per 
minute. 

EFFECT    OF    CONDENSATION. 

No  account  has  been  taken  in  the  foregoing  of  the  effect  of 
condensation  on  the  flow  of  steam.  It  is  assumed  that  pipes  will 
be  covered,  which  will  reduce  this  effect  to  about  one-third  of 
what  it  would  be  if  they  were  bare.  The  condensation,  while  it 
cuts  down  the  volume  of  steam,  at  the  same  time  causes  a  greater 
drop  in  pressure.  This,  in  turn,  increases  the  velocity,  tending  to 


86  -.Principles  of    Heating. 

offset  the  loss  by  Condensation.  A  further  discussion  of  this  sub- 
ject may  be  found  in  Kent's  "Mechanical  Engineers'  Pocket 
Book." 


STEAM   FLOW   WITH   MORE  THAN   40  PER   CENT.   DROP   IN   PRESSURE. 

It  is  to  be  borne  in  mind,  in  making  computations  of  the  flow 
of  steam,  that  steam  of  25  pounds  gauge  pressure  or  more,  dis- 
charged from  a  pipe  against  atmospheric  pressure  or  against  a 
pressure  less  than  three-fifths  the  initial  pressure,  has  a  nearly 
constant  velocity  of  900  feet  per  second,  in  round  numbers,  the 
weight  discharged  increasing  with  the  pressure  and  being  propor- 
tional to  the  density  or  weight  per  cubic  foot.  The  approximate 
weight  of  steam  that  will  flow  per  hour  through  a  pipe  under  the 
conditions  just  stated  is  equal  to  50  X  (absolute  pressure  of 
steam)  X  (area  of  pipe  in  square  inches). 

This  constant  velocity  applies  only  to  very  short  pipes. 

RELATIVE   CAPACITIES   OF   PIPES. 

The  relative  capacities  of  pipes  under  the  same  conditions  are 
shown  in  Table  XVI,  D'Arcy's  values  being  the  safer  to  use.  This 
table  will  be  found  convenient  in  determining  the  size  of  pipe 
necessary  to  supply  a  number  of  smaller  ones. 

Example:  What  size  pipe  is  required  to  supply  one  2^,  two 
3  and  one  4  inch  pipes  ? 

The  capacities  in  Table  XVI  are,  in  the  order  stated,  I  x  n.6, 
2x20.8,  1x41.4;  total,  94.6.  A  6-inch  pipe  with  a  capacity  of 
1 18  should  be  used,  since  a  5-inch  pipe  has  a  capacity  of  only  73. 

It  will  be  noted  that  the  capacity  of  pipes  increases  much  more 
rapidly  than  their  area — e.  g.,  the  relative  capacities  of  8  and  4 
inch  pipes  in  Table  XVI  are  246  and  41.4,  or  in  the  ratio  of  6  to  I, 
whereas  their  areas  are  in  the  ratio  of  about  4  to  I. 

Table  XXI,  which  has  been  computed  from  Table  XVI,  gives 
the  proper  size  of  mains  to  supply  branches  of  the  sizes  stated  in 
the  upper  and  side  lines. 


The   Flow    of   Steam    in    Pipes. 


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88 


Principles    of    Heating. 


SIZES  OF  STEAM    HEATING  MAINS. 

For  steam  heating  work  it  is  generally  more  convenient  to 
deal  with  heat  units  and  the  amount  of  direct  rediating  surface 
that  pipes  of  different  sizes  will  supply,  than  with  the  weight  of 
steam  they  will  carry.  A  conservative  basis  is  to  allow  250  heat 
units  per  hour  per  square  foot  of  ordinary  cast  iron  direct  radiat- 
ing surface,  with  steam  at  low  pressure,  say  3-5  pounds. 

A  pound  of  steam  at  5  pounds  pressure  has  a  latent  heat  of 
954.6  units — that  is,  it  will  give  up  954.6  heat  units  when  con- 
densed to  water  at  the  steam  temperature  in  the  radiator. 

Table  XXII  has  been  deduced  from  the  flow  of  steam  computed 
from  D'Arcy's  formula,  as  stated  in  Table  XVI,  on  the  basis  of  250 
heat  units  per  square  foot  of  radiation  and  954.6  heat  units  given 
off  per  pound  of  steam,  which  is  equivalent  to  0.262  pounds  of 
steam  condensed  per  hour  per  square  foot  of  direct  radiating  sur- 
face. 

TABLE   XXII. 


THE  AMOUNT  OF  ORDINARY  CAST  IRON  RADIATING  SURFACE  THAT  MAY  BE  SUPPLIED 
BY  PIPES  OF  DIFFERENT  SIZES,  100  FEET  LONG,  WITH  5  POUNDS  INITIAL 
GAUGE  PRESSURE  AND  THE  DROP  IN  PRESSURE  STATED  IN  THE  COLUMN  AT  THE 
LEFT.  FOR  OTHER  PRESSURES  AND  FOR  LENGTHS  IN  EXCESS  OF  100  FEET,  USE 
FACTORS  IN  TABLES  XVII  AND  XIX.  RESISTANCE  AT  ENTRANCE,  ELBOWS  AND  GLOBE 
VALVES  MAY  BE  ALLOWED  FOR  AS  STATED  IN  TABLE  XX  BUT  THIS  IS  GENERALLY 
UNNECESSARY  FOR  ORDINARY  WORK,  A  SLIGHT  EXCESS  IN  THE  DROP  IN  PRES- 
SURE OVER  THAT  ASSUMED  COMPENSATING  FOR  THE  RETARDING  EFFECT  OF 
THE  ENTRANCE,  ELBOWS  AND  VALVES. 


Diameter  of  pipes, 
Inches  ........ 


1V2 


Line. 


Drop  in 

pressure. 
Pounds. 


Square  feet  of  radiating  surface. 


A 1     261  545  847  1,535  2,660  4,770  6,950  9,500      12,820 

B %     226  472  732  1,325  2,300  4,120  6,000.  8,210     11.100 

185  386  600  1,087  1,881  3,370  4,930  6,730        9,100 

130  273  423  767  1,330  2,385  3,475  4,750 

92  193  299  543 

65  136  212  384 


D 

E 

F 

i/16 

G.. 

..  V« 

940     1,680     2,460     3,360 
665     1,192     1,740     2,380 


6,210 
4,530 
3.210 


46        96     150         272         470         845     1,230     1,680        2,270 


The   Flow    of   Steam    in   Pipes. 


89 


Diameter  of  pipes, 
inches  5                6                7             8              9 

12 

Line. 
A 

Drop  in 
pressure. 

1     16  710     27,000     39,800     56,300     75,000     100,000 

159,000 
137,500 
112,500 
74,500 
56,200 
39,800 
28,200 

24 

B  

c 

=54      14,450     23,350     34,400     48,750      64,800        86,500 
y,     11,810     19,100     28,200     39,800     53,000        70,800 

D 

14        8,355     13,500     19,900     28,150     37,400        50,000 

E           .     . 

y8       5  900       9,530     14,060     19,900     26,400       35,400 

F 

Via       4,180       6,750       9,950     14,100     18,700       25,000 
Vs*       2,960       4,780        7,050     10,000     13,300        17,700 

G 

Diameter 
laches. 

Line. 

of  pipe, 
14                 16                18                 20                 22 

Drop  in 
pressure. 

.  .  .     .      1       214,000       290,000       398,000       524,000       675,000 

845,000 
730,000 
598,000 
425,000 
298,000 
212,000 

B 

%       186,000      250,000      343,000      453,000      583,000 

(j 

y2      151,000      206,000      282,000      371,000       478,000 

1> 

i/4      107,000      145,000       198,000      262,000      338,000 

E 

V8         75,100       102,500       140,000       185,000      238,000 

F 

.  .  Vie        53,300         72,600         99,000      131,000      169,000 

G  

Vsa         37,900         51,300         70,500         93,000        

NOTE. — Sizes  14  inches  and  larger  are  outside  diameters.  For  sizes  of  returns 
see  note  under  Table  XXIV. 

Table  XXII  shows  a  marked  difference  in  the  amount  of  ra- 
diating surface  that  may  be  applied  with  different  assumed  drops 
in  pressure. 

Mains  may  be  proportioned  as  follows: 

For  systems  trapped  to  an  open  receiver  with  the  heating  sur- 
face located  well  above  same,  a  drop  of  l/±  to  y2  pound  may  be 
allowed. 

For  gravity  return  systems,  where  the  radiators  are  located 
some  distance,  say  5  feet  or  more,  above  the  water  line  in  the 
boiler,  1-16  to  l/%  pound  drop  may  be  assumed  in  proportioning 
the  piping.  Where  the  radiators  are  but  little  above  the  water  line, 
as  in  indirect  systems,  use  1-32  pound  drop. 

When  exhaust  steam  is  used  and  it  is  desired  that  the  minimum 
back  pressure  be  carried  on  the  system,  an  assumed  drop  of  1-32 
to  1-16  pound  may  be  used,  preferably  1-32  pound  drop. 

The  size  of  vertical  pipes  or  overhead  feed  risers  of  single  pipe 
systems  may  be  based  on  line  G,  Table  XXII.  This  will  give  sizes 
corresponding  to  those  based  on  2,  pounds  pressure  with  a  little 
greater  drop  than  1-32  pound,  and  will  be  found  ample  for  exhaust 
steam  heating. 


9o 


Principles    of    Heating. 


In  high  buildings,  with  the  single  pipe  overhead  feed  system, 
the  risers  must  be  very  liberally  proportioned  on  the  lower  stories, 
since  they  must  carry  not  only  steam  to  the  radiators  below,  but 
the  condensation  from  the  radiators  above. 

It  should  be  noted  that  pipe  sizes  based  on  the  recommenda- 
tions just  made  will  be  large  enough  to  supply  steam  at,  say,  2  or 
3  pounds  pressure  to  the  radiating  surface  stated,  but  with  a 
slightly  greater  drop  in  pressure. 

Pipe  sizes  given  in  Table  XXII  to  supply  a  given  radiating  sur- 
face with  steam  at  5  pounds  pressure  will  be  very  nearly  correct 


Branch 


Branch 


THE  METAL  WORKER 


Fig.  31. 


Fig.  32. 


for  higher  pressures  within  the  ordinary  limits  of  steam  heating, 
say  up  to  15  pounds.  This  is  true,  since  the  total  heat  supplied 
by  the  steam  at  higher  pressures,  taking  into  account  its  increased 
weight  and  decreased  latent  heat  just  about  keeps  pace  with  the 
increased  radiation  of  heat. 

SIZES  OF  RISERS ONE-PIPE  SYSTEM. 

The  risers  of  one-pipe  up  feed  steam  heating  systems  must  be 
made  large  enough  to  supply  the  radiators  and  also  permit  the 
condensation  to  return  by  the  same  route.  It  is,  therefore,  well 
to  limit  the  velocity  to,  say,  15  feet  per  second.  On  this  basis. 


The   Flow   of   Steam    in   Pipes.  91 

with  steam  of  2  pounds  pressure,  pipes  will  supply  ordinary  cast 
iron  direct  radiators  as  follows : 


TABLE  XXIII. 

CAPACITY  OF  UP  FEED  RISERS,  ONE-PIPE  SYSTEM. 

Size  of                   Approximate                       Size  of  Approximate 

riser,  one-pipe  sys-      radiating  surf  ace         riser,  one-pipe  sys-  radiating  surf  ace 

tern.— Velocity  steam,    supplied.— Steam,     tern.— Velocity  steam,  supplied.— Steam. 

15  feet  per  second.      '2  pounds  pressure.       1 5  feet  per  second.  2  pounds  pressure. 

Inches.                            Feet.                            Inches.  Feet. 

1  *50                                  2%  300 
1^4                                *90                                  3  460 
IVa                                130                             .     3%  620 

2  210                                    4  800 


*  It  is  advisable  to  make  the  upper  end  of  riser  the  full  size  of  standard  radi- 
ator connections — viz.,  1  inch  up  to  24  feet  and  1*4  inches  for  25  to  60  feet. 

Down  feed  risers  may  be  safely  rated  to  carry  at  least  25  per 
cent,  more  surface  than  stated  in  the  table.  Care  should  be  taken 
to  proportion  the  risers  liberally  near  the  lower  end  to  provide 
for  the  removal  of  condensation. 

Branch  connections  with  radiators  should  be  the  same  size  as 
regular  tapping,  except  when  radiators  are  located  more  than  4  or 
5  feet  from  risers.  In  this  event  the  connections  should  be  in- 
creased one  size  to  lessen  the  velocity  and  permit  the  condensation 
to  easily  flow  back  against  the  current  of  steam. 

It  is  better  to  drip  the  riser  as  indicated  in  Fig.  31  than  as 
shown  in  Fig.  32.  With  the  latter  the  condensation  is  apt  to  be 
swept  up  along  the  heel  of  the  elbow,  causing  a  click,  or  water 
hammer.  The  arrangement  shown  in  Fig.  I  forms  a  separator 
and  the  condensation  trickles  away  quietly  through  the  relief  or 
return  pipe. 

SIZES  OF  RISERS TWO-PIPE  SYSTEM. 

With  the  two-pipe  up  feed  system  risers  may  be  considerably 
smaller  for  a  given  radiating  surface  than  in  the  one-pipe  system, 
since  the  condensation  from  the  radiators  is  conducted  away 
through  separate  returns. 

Table  XXIV  gives  safe  allowances : 


92  Principles    of    Heating. 


TABLE  XXIV. 

CAPACITIES  OF  UP  FEED  RISERS,  TWO-PIPE   SYSTEM. 


Size  of  riser 
for  two-pipe,  up 
feed  steam  heating. 
Inches. 
1 

'        1% 
,.        2 

Approximate 
radiating  surface 
supplied.—  Steam  at 
2  pounds  pressure. 
Feet. 
*70 
*130 
*190 
330 

Size  of  riser 
for  two-pipe  up 
feed  steam  heating. 
Inches. 

'         3  " 

4 

Approximate 
radiating  surface 
supplied.—  Steam  at 
2  pounds  pressure. 
Feet. 
570 
1,020 
1,490 
2,000 

*  It  is  advisable,  at  the  upper  ends  of  long  risers,  to  make  the  riser  the  full 
size  of  standard  radiator  connections — viz.,  1  inch  up  to  48  feet ;  1*4  inches  for 
49  to  96  feet,  and  1%  inches  for  97  and  up  to  190  feet. 

For  down  feed  risers  it  is  safe  to  allow  25  per  cent,  more  sur- 
face than  stated  in  the  above  table. 

In  high  buildings,  say  over  five  or  six  stories,  allow  10  per 
cent,  less  surface  than  that  stated  to  allow  for  the  increased  length 
of  and  condensation  in  risers.  Returns  are  commonly  made  one 
size  smaller  than  the  supply  up  to  2.^/2  inches ;  above  that  the  re- 
turns may  be  two  sizes  smaller,  and  for  larger  pipes,  where  the 
return  has  ample  fall,  it  may  be  made  one-half  the  diameter  of  the 
supply  pipe,  or  even  smaller. 

PIPE   SIZES    FOR   THE   TWO-PIPE   VACUUM    SYSTEM    OF    STEAM 
HEATING. 

Supply  connections  with  radiators  and  coils  in  the  two-pipe 
vacuum  system  of  steam  heating  are  commonly  ^4  mcri  UP  to  50 
square  feet,  I  inch  for  51  to  100  square  feet,  i%  inches  for  101 
to  190  square  feet,  iJ/£  inches  for  191  to  310  square  feet,  2  inches 
for  311  to  670  square  feet,  2.y2  inches  for  671  to  1250  square  feet 
and  3  inches  for  1251  to  2040  square  feet.  It  will  be  noted  that 
these  are  considerably  smaller  than  pipe  connections  with  ordinary 
low  pressure  heating  systems. 

Sizes  of  up  feed  risers  in  buildings  of  six  or  eight  stories  may  be 
based  on  Table  XXII,  line  D.  In  proportioning  risers  in  high  of- 
fice buildings  with  the  down  feed  vacuum  system  Table  XXII,  line 
E,  may  be  used.  The  lower  portion  of  such  risers  should  be  pro- 
portioned to  supply  10  to  15  per  cent,  less  surface  than  that  stated 
in  the  table,  since  they  must  not  only  supply  steam  to  the  radiators, 
but  must  carry  away  the  condensation  from  the  attic  mains  and 


The    Flow    of   Steam    in    Pipes.  93 

from  the  risers  above.    Return  risers  are  very  much  smaller  than 
with  the  ordinary  two-pipe  system. 

The  following  table  gives  safe  allowances  for  horizontal  re- 
turns. These  allowances  may  be  safely  increased  20  to  30  per  cent, 
for  short  lines. 

TABLE   XXV. 

RETURN    PIPE    CAPACITIES    FOR    TWO-PIPE    VACUUM    SYSTEMS. 

Square  feet  of  direct 
radiating  surface 

Size  of                                                                                                           to  which  return 
return  pipe.                                                                                                  pipe  is  adapted. 
%  inch 200 

1  inch 200-      800 

1%  inches 800-  1,500 

iy«  inches 1,500-  3,000 

2  inches .   3,000-  6,000 

2y2  inches 6,000-12,000 

3  inches 12,000-20,000 

3%  indies 20,000-30,000 

4  "  inches 30,000-40,000 

Return  risers  may  be  rated  as  follows : 

%  inch  up  to 1,000  feet. 

1      inch  up  to 1,600  feet. 

IVi  inches  up  to 2,500  feet. 

The  size  of  main  steam  supply  pipes  and  branches  should  be 
based  on  the  distance  of  the  most  remote  radiator  from  the  source 
of  supply,  the  distance  in  overhead  feed  systems  to  be  measured 
from  the  center  of  distribution  in  the  attic.  It  is  not  necessary 
to  add  the  length  of  the  main  exhaust  pipe  from  the  basement, 
since  it  is  merely  a  reservoir  of  steam,  and  distribution  really  be- 
gins at  the  tee  connected  with  the  same  in  the  attic. 

For  lengths  of  100  feet  or  less  pipe  sizes  based  on  line  C  of 
Table  XXII  agree  fairly  closely  with  common  practice  in  this  class 
of  work.  For  other  lengths,  multiply  the  figures  in  line  C  by 
the  factors  in  Table  XIX  in  order  to  ascertain  the  capacity  of  pipes, 
expressed  in  the  square  feet  of  radiating  surface,  they  will  supply. 

Smaller  pipes,  both  for  supply  and  return,  could  be  made  to 
do  the  work  by  carrying  a  few  ounces  more  pressure  on  the  mains 
or  by  causing  the  pumps  to  maintain  a  stronger  pull  on  the  returns. 


94  Principles    of   Heating. 

COMPARISON    OF   DIFFERENT    METHODS    OF    DETERMINING    THE    SIZE 
OF  STEAM  MAINS  TO  SUPPLY  RADIATING  SURFACES. 

In  addition  to  the  foregoing  it  seems  wise  to  reprint  here  an 
article  by  Earnest  T.  Child  that  appeared  under  the  above  head- 
ing in  The  Metal  Worker  of  Aug.  19,  1899. 

The  primary  method  of  figuring  the  sizes  required  is  to  ascer- 
tain the  volume  of  steam  which  will  be  condensed  by  the  radiating 
surface.  This  being  known,  the  size  of  pipe  may  be  computed 
by  assuming  a  velocity  of  flow,  which  will  cause  a  loss  of  pressure 
not  exceeding  12  inches  water  head  per  100  feet  of  pipe ;  say,  a 
velocity  of  50  feet  per  second,  which  will  give  an  approximate 
frictional  resistance  of  8  inches  of  water  per  100  feet. 

For  instance,  to  supply  1000  square  feet  of  radiating  surface 
at  5  pounds  gauge  pressure: 

Temperature    of     steam  =r  227  degrees  F. 
Temperature  of  air  in  room,  70  degrees  F. 


Difference,   air  and   steam,    157  degrees  F. 

British  thermal  units  radiated  per  square  foot  of  surface  as 
per  experiments  by  Wm.  J.  Baldwin,  J.  H.  Mills,  and  others  aver- 
age 275.  This  gives  275,000  British  thermal  units  per  hour.  As 
each  pound  of  steam  at  this  pressure  is  capable  of  yielding  954 
British  thermal  units,  it  will  require  288  pounds  of  steam  per 
hour.  One  cubic  foot  of  steam  at  5  pounds  weighs  0.0511  pounds, 
so  288  pounds  equal  5636  cubic  feet  per  hour,  or  1.56  cubic  feet 
per  second,  which,  flowing  at  the  rate  of  50  feet  per  second,  will 
require  an  area  of  0.0312  square  foot,  or  4.59  square  inches.  This 
would  require  a  pipe  2.4  inches  in  diameter,  and  as  the  next  higher 
commercial  size  is  2l/2  inches  in  diameter,  this  would  be  the  size 
required. 

This  is  a  roundabout  way,  however,  and  various  formulas 
have  been  evolved  for  figuring  the  pipe  sizes. 

Robert  Briggs  in  his  "  Steam  Heating  "  uses  a  formula  which 
has  been  extensively  followed  either  directly  or  in  a  modified 
form,  in  which  d  =  diameter  of  pipe ;  q  =  9.2  cubic  feet  of  steam 


The   Flow    of   Steam    in    Pipes.  95 

per  100  square  feet  radiating  surface ;  /  =  length  of  main  in  feet ; 
and  h  =  head  of  steam  to  produce  the  flow.    From  this 


=  0.5374       -,- 
h 


Frederic  Tudor  uses  a  modified  form  of  the  same,  in  which 
C  =  volume  of  steam  per  minute  —  9.2  X  total  radiating  sur- 
face -f-  100  ;  L  =  length  of  main  in  yards  ;  and  H  =  head  in 
inches  of  water  lost  [loss  in]  pressure;  d  —  diameter  of  pipe. 
From  which 


These  two  formulas,  when  figured  on  a  basis  of  6  inches  lost 
[[loss  in]  pressure  in  a  loo-foot  run,  agree  very  closely. 

A  rule  given  by  Wm.  J.  Baldwin  in  his  "  Steam  Heating  for 
Buildings,"  and  also  published  by  Geo.  H.  Babcock,  states  that 
diameter  of  main  in  inches  should  equal  one-tenth  of  the  square 
root  of  the  total  radiating  surface,  mains  included.  This  rule, 
when  compared  with  the  two  previous  ones,  provides  for  a  much 
more  ample  pipe,  and  on  systems  of  over  4000  square  feet  it 
would  be  safe  to  use  on  mains  as  long  as  600  feet,  though  it  does 
not  primarily  take  in  the  element  of  distance  at  all.  Even  for 
smaller  systems  it  gives  a  relatively  large  diameter,  and  for  10,000 
square  feet  of  surface  it  gives  a  diameter  fully  35  per  cent,  larger 
than  the  best  accepted  practice,  which  means  an  area  which  is 
nearly  doubled. 

A.  R.  Wolff,  in  his  "  Addendum  to  Steam  Heating  "  by  Briggs, 
gives  the  following:  "For  determining  the  cross  section  area  of 
pipes  (in  square  inches)  for  steam  mains  and  returns,  it  will  be 
ample  to  allow  a  constant  of  0.375  square  inch  in  coils  and  radia- 
tors, 0.375  square  inch  when  exhaust  steam  is  used,  0.19  square 
inch  when  live  steam  is  used  and  0.09  square  inch  for  the  return 
for  each  100  square  feet  of  heating  surface.  If  the  cross  sectional 
areas  thus  obtained  are  each  multiplied  by  one  and  three-elevenths. 
and  the  square  root  extracted  from  each  product,  the  respective 
figures  will  represent  the  proper  diameters  in  inches  of  the  several 
,steam  pipes  referred  to.  The  steam  mains  should  never  be  less 


g6  Principles    of    Heating. 

than  il/2  inches  in  diameter,  nor  the  returns  less  than  y^  inch  in 
diameter." 

This  rule  does  not  take  into  account  the  relative  decrease  in 
friction  in  pipes  of  larger  diameters,  and  while  in  systems  under 
2500  square  feet  it  follows  the  Briggs  and  Tudor  formulas  very 
closely,  on  larger  areas  it  goes  up  more  rapidly  on  account  of  the 
fact  that  the  area  of  the  main  is  directly  proportional  to  the  area 
of  the  radiating  surface.  This  formula  is  safe  to  use  for  mains 
under  200  feet  in  length,  but  if  this  be  exceeded  the  area  should 
be  proportionally  increased. 

Prof.  R.  C.  Carpenter,  in  his  "  Treatise  on  Heating  and  Ven- 
tilating Buildings,"  uses  Briggs'  formula,  with  the  exception  that 
for  a  frictional  resistance  of  6  inches  water  column  he  uses  the 
value  of  318.6  for  H  instead  of  477.8,  which  gives  a  50  per  cent, 
larger  area  of  main ;  but  as  this  table  is  figured  for  a  single  pipe 
system,  50  per  cent,  larger  areas  will,  of  course,  be  necessary. 
In  figuring  for  a  separate  return  he  uses  the  Briggs  formula  with- 
out change.  His  rule  for  bends  and  obstructions  is  as  follows: 
"  Right  angle  ells  add  40  diameters ;  globe  valve,  60  diameters ; 
entrance  tee,  60  diameters.  For  other  resistances  and  steam  pres- 
sures multiply  the  diameters  by  the  following  factors : 

Water  level  above  boiler 2  inches.  12  inches.  18  Inches. 

Multiply    by 1.25  0.88  0.80 

Steam   pressure  above   atmosphere 0  pound.  3  pounds.  30  pounds. 

Multiply    by 1.03  1.02  0.97 

For  indirect  heating  with  separate  return  use  the  result  as  ob- 
tained." 

The  result  of  the  above  formula  when  plotted  gives  diameters 
about  Y-2  inch  larger  than  A.  R.  Wolff's  rule  up  to  5000  square 
feet,  and  at  about  7600  square  feet  the  lines  across  (see  chart). 
On  the  other  hand,  when  the  "  double  pipe  system  "  line  is  plotted, 
it  follows  the  Wolff  and  Tudor  curves  quite  closely  up  to  4000 
square  feet,  and  at  7000  square  feet  it  drops  below  them  all. 

The  results  of  all  the  above  formulas  have  been  plotted  on  a 
chart  presented  herewith,  and  it  will  be  seen  that  for  practical  work 
as  well  as  handiness  in  figuring  and  ease  in  remembering  a  simple 
formula,  A.  R.  Wolff's  rule  of  0.375  square  inch  per  100  square 
feet  of  surface  is  best  adapted  to  ordinary  conditions  of  low  pres- 
sure heating. 


The   Flozv    of   Steam    in    Pipes. 


97 


A  line  for  sizes  of  returns  has  also  been  plotted,  based  on  o.i 
square  inch  for  each  100  square  feet  of  surface.  This  gives  an 
area  about  1 1  per  cent,  larger  than  that  used  by  Mr.  Wolff ;  but 


DIAMETER  OF  STEAM   MAfN 

to  *«• 


it  will  be  noticed  that  the  results  are  very  nearly  in  line  with  the 
best  practice. 

Various  rules  for  pipe  sizes  may  be  found,  all  of  which  vary 
in  a  greater  or  less  degree,  and  seem  to  have  been  arrived  at  in  a 


-98  Principles    of    Heating. 

more  or  less  roundabout  way,  or  by  some  rule  of  thumb.  To 
illustrate  the  range  covered  by  these  rules  a  comparative  table  is 
.given  herewith,  which  may  prove  interesting: 

TABLE  XXVI. 

DIAMETER    OP    PIPE    AND    NUMBER    OF    SQUARE    FEET    SUPPLIED. 

Name.                    1-inch,  l^-inoh.  1%-inch.  2-inch.  2V2-inch.  3-inch.  3^-inch. 

Billings    ..  225            450            700  1,200  1,500 

Tudor    40  80  360            320            640  1,280              

Nason    125  200            500  1,000  1,500  2,500 

Willett    40  70  110            220            360  560  810 

Wolff   60  120  200            480            880  1,500             

Billings,  in  his  "  Ventilating  and  Heating,"  states  that  the  only 
objection  to  having  steam  mains  large  is  increased  first  cost,  but 
this  is  a  poor  argument  for  an  engineer  to  set  forth,  as  it  is  his 
business  to  design  a  system  which  will  give  the  best  and  most  eco- 
nomical results  at  a  moderate  first  cost.  He  also  overlooks  the 
fact  that  larger  pipes  cause  a  greater  loss  by  radiation. 

The  sizes  used  by  Frederic  Tudor  are  for  connections  to  radia- 
tors only,  the  mains  being  determined  by  the  formula  previously 
stated.  This  is  a  simple  rule,  and  has  been  proven  very  satisfac- 
tory. He  allows  40  square  feet  radiation  for  each  i-inch  pipe, 
and  doubles  the  figure  for  each  successive  size  up  to  3  inches. 

The  sizes  given  by  J.  R.  Willett  are  very  large  indeed  compared 
with  other  authorities,  and  are  not  to  be  recommended. 

The  sizes  used  by  the  Nason  Mfg.  Company  and  A.  R.  Wolff, 
as  given  on  pages  540  and  541  of  Kent's  Handbook,  are  almost 
identical.  Of  these  five  cases  the  rule  used  by  Tudor  appeals  to 
the  writer  [E.  T.  Child]  as  being  the  simplest  and  most  practical, 
in  that  it  is  easily  applied  and  not  easily  forgotten;  and  while  it 
gives  sizes  which  are  ample  to  fulfill  the  requirements  it  does  not 
overdo  the  matter.  Of  course  single  radiators  seldom  aggregate 
more  than  300  square  feet  on  direct  work,  and  it  will  be  noted  that 
up  to  this  size  there  is  very  little  variation  in  the  sizes  used  by  all. 

The  formulas  given  in  the  foregoing  relate  entirely  to  direct 
radiation.  It  has  been  found  that  indirect  stacks  condense  from  50 
to  loo  per  cent,  more  steam  than  direct,  depending  upon  the  ve- 
locity of  the  air  passing  over  them,  other  conditions  being  the 
same.  R.  C.  Carpenter  states  in  his  "  Heating  and  Ventilating 
Buildings  " : 


The   Flow    of   Steam    in    Pipes.  99 

"  The  indirect  heating  surfaces  require  about  twice  as  much 
heat  as  the  same  quantity  of  direct  radiating  surface,  and  hence, 
for  same  resistance  in  the  pipe,  the  area  should  be  twice  that  re- 
quired in  direct  heating.  It  will  usually  be  sufficiently  accurate  to 
use  a  pipe  the  diameter  of  which  is  1.4  times  greater  than  that  for 
direct  heating."  But  he  makes  a  statement  earlier  in  the  book  that 
for  indirect  heating  with  separate  return  an  area  50  per  cent,  larger 
than  that  used  for  direct  heating  will  be  sufficient.  To  cover  all 
contingencies,  however,  it  will  be  safe  to  figure  an  area  twice  as 
large  as  for  direct,  and  the  same  rule,  of  course,  applies  to  the 
return. 

Indirect  heaters,  when  used  in  connection  with  a  fan,  condense 
even  more  steam  than  when  operated  under  natural  draft,  on 
account  of  the  greater  velocity  bringing  more  air  into  contact  with 
the  radiating  surface  in  a  given  time.  The  quantity  of  steam 
which  will  be  condensed  in  them  under  these  conditions  is,  how- 
ever, a  decidedly  variable  quantity.  Suppose,  for  instance,  that 
the  air  entering  the  heater  is  at  o  degrees  F.,  then  the  condensation 
will  be  36  per  cent,  greater  than  it  would  if  air  were  returned 
from  the  building  at  60  degrees  F. ;  velocity  being-  constant  and 
steam  pressure  5  pounds  gauge.  If  the  velocity  of  air  passing 
through  the  heater  changes  from  750  to  1500  feet  per  minute 
there  will  be  a  further  increase  of  at  least  30  per  cent. ;  making  a 
total  variation  of  about  77  per  cent,  in  the  amount  of  steam  con- 
densed. ].  H.  Mills  states  that  1000  cubic  feet  of  air  passing  over 
each  square  foot  of  surface  will  cause  it  to  condense  from  900  to 
1300  British  thermal  units. 

LOW    PRESSURE    HEATING    MAINS. 

The  following  extracts  from  an  article  by  C.  E.,  which  ap- 
peared in  The  Metal  Worker  of  June  25,  1904,  are  reprinted  here 
as  adding  something  to  the  general  fund  of  information  on  this 
subject: 

"  Gradually  a  set  of  rules  for  accurately  determining  the  size  of 
steam  mains  is  being  evolved.  One  of  the  earliest  of  these,  and 
one  of  the  most  extensively  used,  states  that  a  square  inch  of  free 
cross  sectional  area  in  a  steam  pipe  will  supply  100  square  feet  of 
radiating  surface.  This  rule  is  qualified  by  its  originator  in  many 
different  ways,  so  much  so  that  he  is  reputed  to  have  said  that  if 


TOO  Princ'>l-"s    of   Heating. 

a  pipe  proved  too  small  to  double  its  size.  This  rule  totally  ne- 
glects the  varying  amount  of  frictional  resistance  between  large 
and  small  pipes.  It  is  rather  absurd,  of  course,  to  assume  that  the 
carrying  capacity  of  an  8-inch  pipe  can  be  computed  by  the  same 
rule  as  a  I ^4 -inch  pipe." 

There  are  numerous  other  rules  which  have  appeared  in  the 
more  recent  scientific  books,  all  of  which  are  helpful  in  their  way, 
but  none  of  which  is  in  very  general  use  among  engineers,  owing 
to  the  fact  that  they  cannot  be  applied  to  pipes  of  all  sizes. 

Probably  one  of  the  safest  rules  in  calculating  the  size  of  a 
steam  heating  main  is  that  in  common  use  among  engine  builders 
— that  is,  basing  the  size  of  the  pipe  to  give  an  arbitrary  velocity 
of  steam  flowing  through.  In  high  pressure  work  the  safe  veloci- 
ties are  well  known;  but  in  low  pressure  work  this  is  not  so,  as 
there  are  only  a  few  offices  in  which  this  method  of  calculating 
sizes  has  been  experimentally  reduced  to  a  comparatively  exact 
science  and  in  which  the  safe  velocities  for  various  sizes  of  pipes 
used  for  different  purposes  are  definitely  known. 

The  basis,  of  course,  for  any  such  rule  must  be  the  amount  of 
steam  condensed  by  a  direct  radiator  of  the  usual  type  working 
under  normal  conditions  with  the  outside  temparature  at  zero. 
After  an  exhaustive  series  of  experiments  it  has  been  determined 
that  this  will  amount  to  approximately  0.3  pound  of  steam  con- 
densed per  hour  per  square  foot  of  radiating  surface.  This 
amount,  0.3  pound,  is  based  on  using  steam  at  zero  pressure ;  but. 
as  the  ordinary  steam  heating  plant  is  designed  to  operate  at  i 
to  10  pounds  pressure,  the  difference  in  the  amount  of  condensa- 
tion at  pressures  within  that  range,  although  considerable,  would 
not  be  enough  to  overload  liberally  designed  piping. 

Given  the  square  feet  of  heating  surface,  the  cubic  feet  of  i 
pound  of  steam  and  the  safe  velocity,  it  is  an  easy  matter  to  deter- 
mine the  size  of  the  piping.  The  only  difficult  part  is  to  determine 
what  is  the  safe  velocity  for  a  given  condition.  No  set  of  calcula- 
tions, no  matter  how  elaborate,  will  give  this;  nor  can  one  fall 
back  on  the  experience  of  the  steam  fitter,  as  he  hasn't  the  slightest 
idea  how  fast  the  steam  is  going. 

The  best  sources  of  information  available  indicate  that  the  fol- 
lowing velocities  are  safe.  They  are  based  on  extensive  experi- 


The   Flow    of   Steam    in    Pipes.  101 

ments  and  observations  among  old  buildings  in  which  the  piping 
is  very  small :  A  velocity  of  80  feet  per  second  is  perfectly  safe  in 
mains  2  to  3^  inches,  inclusive.  On  mains  of  these  sizes  the  fric- 
tional  resistance  is  rather  high,  so  that  the  velocity  used  is  low. 
Still,  even  at  that,  a  3-inch  main  will  supply  1800  square  feet  of 
direct  radiation.  According  to  the  old  rule  of  a  square  inch  of 
area  to  100  square  feet  of  surface,  the  same  pipe  would  supply  onlv 
about  750  square  feet — rather  a  wide  variation  between  two  rules ; 
yet  the  former  has  been  demonstrated  time  and  again  to  be  per- 
fectly true. 

For  il/4  and  i^inch  mains  the  safe  velocity  is  hardly  more 
than  50  feet  per  second;  but,  as  a  matter  of  practice,  these  sizes 
are  rarely  used  with  any  but  an  arbitrary  amount  of  radiation, 
depending  on  local  conditions.  At  50  feet  velocity  a  il/2 -inch  pipe 
will  supply  300  square  feet  of  radiation.  A  velocity  of  90  feet  is 
low  enough  for  4  to  6  inch  pipe,  inclusive.  On  this  basis  a  5-inch 
main  will  supply  5700  square  feet.  This  is  probably  considerably 
more  than  current  practice  among  steam  fitters  allows.  On  pipes 
larger  than  6  inches  a  velocity  ranging  from  95  to  100  feet  per 
second  is  considered  good  practice.  An  8-inch  pipe  at  100  feet 
velocity  will  carry  about  15,000  square  feet  of  direct  radiation, 
and  a  1 2-inch  pipe  about  35,000  square  feet. 

It  is  presumed,  of  course,  in  giving  the  above  figures  that  the 
pipes  are  insulated  with  a  fair  make  of  covering  and  that  they  are 
reasonably  dripped. 

An  elaborate  system  of  drips  is  not  essential,  but  the  impor- 
tance of  a  reasonable  dripping  cannot  be  overestimated.  A  main 
cannot  be  expected  to  carry  its  maximum  amount  of  surface  if  in 
addition  it  must  carry  the  condensation  from  a  long  system  of 
mains.  Furthermore,  it  is  necessary  that  the  drips  be  made  in  a 
way  that  will  avoid  any  churning  of  water  in  the  fittings  at  the 
drips.  There  is  nothing  so  fatal  to  the  capacity  of  a  main  as  the 
churning  and  splashing  caused  by  badly  made  drips  and  by  wrong 
pitch. 

For  continuous  circuit  main  work,  so  largely  used  nowadays, 
especially  in  the  smaller  class  of  buildings,  it  is  necessary  to  provide 
carrying  capacity  in  the  mains  for  the  entire  amount  of  condensa- 
tion as  well  as  the  steam,  although  it  may  be  urged  that  as  the 


io2  Principles    of    Heating, 

amount  of  water  increases  the  amount  of  steam  decreases.  Still  it 
is  usual  to  make  large  allowance  for  the  water  in  this  class  of 
work,  using  a  velocity  of  about  60  feet  for  the  smaller  size  mains 
and  70  feet  for  the  larger  sizes.  On  this  basis  a  5-inch  continuous 
circuit  main  will  supply  about  4000  square  feet  of  radiation. 

The  proper  proportioning  of  the  risers  in  a  heating  plant  is 
probably  the  most  difficult  part.  It  is  of  course  fatal  to  the  entire 
apparatus  to  get  them  too  small ;  and,  at  the  same  time,  structural 
conditions  usually,  and  the  wishes  of  the  architect  or  owner,  neces- 
sitate making  them  as  small  as  possible.  A  low  velocity  must  be 
used  on  account  of  the  reverse  flow  of  water ;  much  more  serious 
in  one-pipe  work  than  in  two-pipe.  A  velocity  of  40  feet  per 
second  is  perfectly  safe  on  one-pipe  risers  and  50  feet  for  two-pipe 
risers.  On  this  basis  a  2^-inch  one-pipe  riser  will  supply  600 
square  feet  of  radiation  and  2l/2 -inch  two-pipe  riser  about  750 
square  feet.  These  figures  may  seem  excessive,  but  they  are  con- 
stantly in  use  and  give  excellent  results.  [These  are  greatly  in 
excess  of  the  capacities  given  in  Tables  XXIII  and  XXIV.] 

No  set  velocities  for  radiator  connections  can  be  given,  as  these 
are  determined  arbitrarily  by  good  practice,  it  being  necessary  to 
make  allowance  for  many  other  things  besides  the  amount  of 
steam  a  connection  will  normally  carry.  The  sizes  are  well  known 
and  will  not  be  repeated  here. 

It  is  essential,  in  designing  any  steam  heating  apparatus,  to 
provide  for  the  very  heavy  demand  for  steam  when  the  plant  is 
put  in  operation  in  the  morning.  The  effect  of  this,  of  course,  is 
to  increase  the  velocities,  which  effect  is  most  troublesome  in  the 
risers  and  radiator  connections.  The  velocities  as  given  above  are 
sufficiently  low  to  provide  for  this,  so  that  no  further  allowance 
need  be  made.  It  will  be  noticed  that  the  risers  will  be  far  larger 
than  the  mains  in  proportion  to  the  amount  of  steam  they  carry. 
Radiator  connections  in  good  practice  are  made  larger  than  any 
possible  demand  for  steam  would  necessitate. 

SIZES  OF  MAIN  STEAM    PIPE  CONNECTIONS  WITH  BOILERS. 

Suppose  a  boiler  is  supplying  steam  to  an  engine  cutting  off  at,, 
say,  one-third  of  the  stroke — that  is,  admitting  steam  about  one- 
third  of  the  time?  Assuming  a  maximum  velocity  in  the  supply 


The   Flow    of    Steam    in    Pipes.  103 

pipe  of  6000  feet  per  minute,  if  steam  is  passing  through  the  same 
only  one-third  of  the  time,  the  average  velocity  will  be  2000  feet 
per  minute.  Basing  the  size  of  main  steam  connections  with  boil- 
ers on  this  velocity  gives  the  following  size  pipes  when  the  steam 
pressure  is  80  pounds.  The  pipe  sizes  for  higher  pressures  would, 
of  course,  be  smaller  if  computed  in  the  same  manner,  but  it  is 
advisable  to  use  as  large  pipes  as  those  stated  in  the  table,  which 
conform  pretty  closely  with  present  boiler  practice: 

TABLE  XXVII. 

SIZE     OF     MAIN     STEAM      PIPES      FOR     BOILERS     OF     HORSE-POWER      STATED. STEAM 

7RESSURE   ASSUMED   TO   BE    80   POUNDS    BY    GAUGE  ;    AVERAGE    VELOCITY    IN    PIPE, 
2000   FEET   PER   MINUTE. 

Size  of  pipe 

Boiler  Pipe  area.  corresponding, 

horse-power.  Square  feet.  Inches. 

50  0.057  3 

62%  0.071  3V2 

75  0.085  4 

100  0.114  4% 

125  0.142  5 

150  0.171  6 

200  0.228  7 

250  0.285  8 

300  0.342  8 

NOTE. — Four  and  one-half  inch  pipes  and  valves  being  an  odd  size,  it  is  advis- 
able to  use  5-inch  instead.  When  globe  valves  are  used  in  boiler  connections,  It  Is 
well  to  make  the  pipes  one  size  larger  than  when  straightway  gate  valves  are 
used,  to  compensate  for  the  increased  resistance. 

SIZES   OF   STEAM    AND   EXHAUST   PIPES   FOR   ENGINES. 

The  steam  ports  and  supply  pipes  to  engines  are  commonly 
proportioned  on  a  basis  of  a  maximum  velocity  flow  of  6000 
feet  per  minute.  A  simple  automatic  or  throttling  engine  running 
on,  say,  80  pounds  steam  pressure  and  taking  30  pounds  of  steam 
per  horse-power  per  hour  would  require  about  137  cubic  feet  of 
steam  at  the  pressure  stated  for  each  horse-power  per  hour.  The 
admission  of  steam  is  cut  off  anywhere  from  one-quarter  to  three- 
quarter  stroke;  seldom  over  one-half  stroke,  unless  the  engine  is 
very  much  overloaded.  If  we  assume  a  cut-off  of  four-tenths  of 
the  stroke  as  a  fair  basis  on  which  to  compute  the  horse-power  for 
pipes  of  different  sizes  we  have  under  these  conditions  the  capaci- 
ties stated  in  the  following  table. 


104  Principles    of   Heating. 


TABLE  XXVIII. 

SIZES    OP    SUPPLY    PIPES    FOR    STEAM    ENGINES. 

Nominal  diameter  Engine  horse- 

o.f  pipe  in  inches.  power  supplied. 

2 24 

2y2 35 

3 54 

3% 72 

4 92 

4% 117 

5 145 

6 210 

7 .  .   283 

8 364 

Engines  exhaust  during  almost  the  entire  stroke — say  95  per 
cent,  as  a  fair  average.  On  this  basis,  assuming  I  pound  back 
pressure,  30  pounds  steam  per  horse-power  per  hour  and  a  maxi- 
mum velocity  through  the  exhaust  pipe  of  5000  feet  per  minute, 
the  appropriate  horse-power  for  exhaust  pipes  of  given  sizes  has 
been  computed  and  is  stated  in  the  following  table :  [4000  feet 
velocity  is  a  not  uncommon  velocity  to  assume.] 

TABLE   XXIX. 

SIZES   OF  EXHAUST   PIPES   FOR   STEAM    ENGINES. 


Nominal  diam- 
eter of  exhaust 
pipe  in  inches. 

2y» 

Engine 
horse-power. 
20 

3 

30 

314 

40 

4 

50 

4U 

.                63 

5 

80 

6  

115 

153 

8  

200 

10.. 

.     312 

A  comparison  of  Tables  XXVIII  and  XXIX  shows  the  size 
exhaust  pipe  for  a  given  horse-power  to  be  one  size  larger  than 
the  steam  pipe,  which  accords  very  well  with  the  general  prac- 
tice of  engine  builders.  Some  engine  builders  make  their  steam 
and  exhaust  connections  abnormally  large  to  provide  for  cases 
where  the  pipe  lines  are  long.  The'  foregoing  tables  give  permis- 
sible sizes  that  may  be  used  in  proportioning  the  piping  in  office 
and  other  buildings  having  individual  or  isolated  mechanical 
plants. 


The   Flow   of   Steam   in   Pipes.  105 

EFFECT  OF  BACK  PRESSURE  ON  SIMPLE  AUTOMATIC  ENGINES. 

With  a  simple  automatic  engine  carrying  a  back  pressure  of  5 
pounds  the  loss  in  power  due  to  back  pressure  will  be  as  follows : 
Take,  for  example,  a  high. speed  engine  commonly  used  to  drive 
a  direct  connected  dynamo.  With  90  pounds  initial  gauge  pres- 
sure, equal  to  about  105  pounds  absolute  pressure,  and  steam 
cut  off  at  one-quarter  stroke,  the  average  pressure  per  square 
inch  on  the  pushing  side  of  the  piston  throughout  the  stroke  will 
be  about  63  pounds. 

From  this  must  be  deducted  the  atmospheric  pressure,  equal  to 
15  pounds  per'square  inch,  or  say  16  pounds,  to  allow  for  the  re- 
sistance of  the  exhaust  pipe  and  elbows.  The  mean  effective  pres- 
sure, equal  to  the  average  pressure  on  the  pushing  side  of  the 
piston  minus  that  on  the  exhausting  side  is  63  —  16  =  47  pounds. 
Now  with  5  pounds  back  pressure,  or  a  total  of  20  pounds  above 
a  vacuum,  the  steam  pressure  on  the  pushing  side  remaining  the 
same,  the  mean  effective  pressure  will  be  63  —  20  =  43  pounds. 
The  horse-power  will  be  in  proportion  to  the  mean  effective  pres- 
sures computed  above ;  that  is,  with  5  pounds  back  pressure  the 
engine  will  have  only  43-47^5  or  91^  per  cent,  of  the  horse- 
power it  has  when  exhausting  freely  to  the  atmosphere.  In  other 
words  the  loss  in  power  due  to  the  back  pressure  would  be  nearly 
9  per  cent. 

EFFECT  OF  BACK  PRESSURE  ON  COMPOUND  ENGINES. 

The  effect  of  back  pressure  is  a  more  serious  matter  in  the  case 
of  compound  engines  than  with  simple  ones,  since  it  acts  on  the 
relatively  large  area  of  the  low  pressure  piston.  To  show  to  what 
extent  the  engine  horse-power  is  reduced  by  a  5-pound  back  pres- 
sure on  a  compound  engine,  take  for  example  an  engine  with  a 
1 6-inch  high  pressure  cylinder,  a  24-inch  low  pressure  cylinder  and 
a  i6-inch  stroke.  A  5-pound  back  pressure  exerted  over  the  large 
area  of  the  low  pressure  piston  would  with  a  piston  speed  of  600 
feet  per  minute  amount  to  452  (square  inches)  X  5  (pounds)  X 
600  (feet)  -f-  33,000  (foot  pounds  per  horse-power)  =41  horse- 
power. Such  an  engine  with  125  pounds  gauge  pressure  when  run 
non-condensing  is  rated  to  develop  about  225  horse-power,  hence 
an  increase  in  the  back  pressure  of  5  pounds  decreases  the  effective 
output  of  the  engine  about  one-fifth  or  20  per  cent. 


io6  Principles    of    Heating. 

COUNTERACTING   BACK    PRESSURE   BY   INCREASED   BOILER    PRESSURE. 

With  a  back  pressure  exhaust  heating  system  either  larger 
engines  must  be  used  to  secure  a  given  horse-power  or  a  higher 
boiler  pressure  must  be  carried.  If  the  latter  is  done  considerably 
more  than  the  5  pounds  back  pressure  commonly  allowed  on  the 
engine  must  be  added  to  the  boiler  pressure,  since  the  back  pres- 
sure is  maintained  throughout  the  stroke  of  the  engine,  but  the 
boiler  pressure  is  cut  off  at  one-quarter,  one-third,  or  some  other 
point  of  the  stroke,  as  the  case  may  be.  To  counteract  5  pounds 
added  to  the  back  pressure  of  an  engine  cutting  off  at  one-quarter 
stroke  about  8  pounds  must  be  added  to  the  boiler  pressure.  A 
few  pounds  added  in  this  way  is  not  a  serious  matter  so  far  as  fuel 
consumption  is  concerned,  since  the  total. heat  necessary  to  make 
steam  increases  very  slowly  with  an  increase  in  pressure  and  not 
at  all  in  proportion  to  the  pressure  increase.  With  ordinary  tubular 
boilers,  however,  the  allowable  pressure  that  may  be  carried  is  cut 
down  from  time  to  time  by  the  insurance  companies,  so  that  if  10 
pounds  more  pressure  must  be  carried,  for  example,  to  overcome  a 
certain  back  pressure  than  would  otherwise  be  necessary,  the  boiler 
must  be  condemned  so  much  the  sooner. 

STEAM   HEATING  IN  CONNECTION  WITH  CONDENSING  ENGINES. 

In  the  case  of  plants  having  condensing  engines,  either  simple 
or  compound,  the  question  arises  whether  it  is  better  economy  to 
run  the  engines  noncondensing  part  of  the  time  and  heat  with  the 
exhaust  steam,  or  to  always  run  them  condensing  and  heat  with 
live  steam.  Which  is  the  better  policy  depends  chiefly  on  the 
amount  of  steam  required  for  heating  in  comparison  with'the  total 
exhaust  from  the  engines.  If  the  amount  is  very  small  manifestly 
it  would  be  better  to  run  condensing  and  secure  the  marked  sav- 
ing in  steam  and  supply  the  heating  system  with  live  steam 
through  a  reducing  valve.  When  there  are  several  engines  it  is 
well  to  have  the  exhaust  pipes  connect  with  a  header  with*cut-out 
valves  between  the  engines,  one  end  of  the  header  connecting  with 
the  condenser  and  the  other  with  the  line  leading  to  the  heating 
system.  Then  one,  two  or  more  engines  may  be  run  condensing 
and  the  others  exhaust  to  the  heating  system. 

As  to  the  economy :  Suppose  a  compound  condensing  engine 
will  develop  an  indicated  horse-power  with  the  consumption  of 


The   Flow    of    Steam    in    Pipes.  107 


1  6  pounds  of  steam  per  horse-power  per  hour,  and  will  require  23 
pounds  of  steam  to  develop  a  horse-power  when  running  non- 
condensing,  a  difference  of  7  pounds.  Under  the  conditions  stated 
a  300  horse-power  engine  would  consume  when  running  noncon- 
densing  300  x  23  =  6900  pounds  per  hour.  If  the  engine  were 
run  condensing  it  would  consume  300  x  16  =  4800  pounds.  In 
the  case  assumed  whenever  more  than  6900  —  4800  =  2100 
pounds  of  steam  per  hour  are  required  by  the  heating  system  it 
will  be  cheaper  to  run  noncondensing. 

Suppose  for  example  that  3600  pounds  of  steam  are  necessary 
to  supply  the  heating  system  for  one  hour.  If  the  engine  is  run 
condensing  4800  pounds  of  exhaust  steam  will  be  condensed  and 
3600  pounds  of  live  steam  must  be  supplied,  a  total  of  8400  pounds 
in  one  hour,  whereas  if  the  engine  were  run  noncondensing  6900 
pounds  of  exhaust  steam  would  be  secured,  of  which  3600  would 
be  used  for  heating,  the  rest  escaping  through  the  exhaust  head, 
except  that  utilized  in  heating  the  feed-water. 

With  the  steam  consumption  assumed,  whenever  more  than  7 
pounds  of  steam  may  be  utilized  in  the  heating  system  to  each 
horse-power  developed  by  the  engine  it  would  be  better  economy 
to  run  noncondensing.  When  less  than  7  pounds  is  needed  the 
engine  should  be  run  condensing.  For  example,  suppose  steam  is 
required  by  the  heating  system  at  the  rate  of  4  pounds  to  each 
horse-power  developed  by  the  engine,  one  horse-power  condensing 
will  take  16  pounds  of  steam,  which,  plus  the  4  pounds  of  Irve 
steam  supplied  to  the  heating  system,  amount  to  20  pounds  per 
engine  horse-power,  whereas  if  the  engine  were  run  noncondens- 
ing 23  pounds  would  be  consumed.  Against  this  method  of  heat- 
ing must  be  charged  the  larger  size  engine  required  to  produce  a 
given  horse-power  when  running  noncondensing. 

In  the  case  of  a  Corliss  simple  noncondensing  engine  taking, 
say,  26  pounds  of  steam  per  horse-power  per  hour  and  21  pounds 
when  condensing,  it  will  be  found  cheaper  to  run  noncondensing 
whenever  the  heating  demands  more  than  5  pounds  of  steam  to 
each  horse-power  developed  by  the  engine  ;  in  other  words,  when- 
ever the  steam  for  heating  exceeds  more  than  about  one-fourth 
that  for  power  it  will  be  better  economy  to  run  nonoondensing, 
and  when  less  than  that  amount  to  run  condensing. 


CHAPTER  X. 
CAPACITIES  OF  PIPES  FOR  HOT  WATER  HEATING. 

THE   FLOW   OF   WATER   IN   PIPES. 

The  force  causing  circulation  in  a  hot  water  heating  system, 
due  to  the  difference  in  temperature  of  the  water  in  the  supply 
and  return  pipes,  is  very  slight  and  amounts  to  only  i  grain,  or 
1-7000  pound  per  square  inch  per  degree  difference  in  tempera- 


Pig.  33. — Head  of  Water  Causing  Flow. 

ture  per  foot  of  hight.  In  ordinary  two-pipe  up-feed  systems  the 
hight  is  to  be  considered  as  that  between  the  middle  of  the  boiler 
and  that  of  the  topmost  radiator.  Suppose  the  supply  and  return 
risers  to  be  25  feet  high  with  20  degrees  difference  in  temperature, 
then  the  excess  of  weight  in  the  return  over  that  in  the  supply 
line  will  be  25  X  20  =  500  grains  =1-14  pound  for  each  square 

108 


Capacities   of   Pipes   for   Hot    Water   Heating.         109 

inch  cross  sectional  area.  Since  I  pound  pressure  is  equivalent 
to  about  2.3  feet,  1-14  pound  is  equal  to  a  head  of,  approximate- 
ly, 0.165  feet,  or  about  2  inches. 

Put  in  another  way,  let  H  in  the  accompanying  sketch  repre- 
sent the  hight  of  a  column  of  water  at  170  degrees  and  h  the 
hight  of  a  column  of  equivalent  weight  at  150  degrees.  Let 
H  =  25  feet,  then 

,  25  X  60.801  (weight  of  i  cubic  foot  at  170  degrees) 

61.204  (weight  of  i  cubic  foot  at  150  degrees) 
=  24.835  feet.   Then,  H  —  h,  the  hight  representing  the  head  or 
unbalanced  force  causing  circulation  of  the  water,  is  0.165  foot, 
or  about  2  inches,  as  above. 

Were  it  not  for  friction  the  velocity  corresponding  to  this 
head  would  be  about  195  feet  per  minute,  since  the  velocity  in 
feet  per  second,  neglecting  friction,  is  approximately  eight  times 
the  square  root  of  the  head,  expressed  in  feet.  Friction,  however, 
plays  a  very  important  part  in  the  laws  governing  the  flow  of 
water  in  pipes,  and  the  actual  velocity  is  only  a  fraction  of  the 
theoretical  velocity,  computed  as  above.  The  resistance  to  the 
flow  is  proportional  to  the  length  of  the  pipe  to  the  square  of  the 
velocity,  and  decreases  as  the  diameter  increases.  That  is,  the 
resistance  varies  inversely  as  the  diameters. 

VOLUME  OF  WATER  TO  SUPPLY  RADIATORS. 

The  volume  of  water  that  must  pass  through  a  radiator  of  a 
given  size  to  maintain  a  certain  output  of  heat  may  be  determined 
as  follows:  Take,  for  example,  a  direct  radiator  of  100  square 
feet,  in  which  the  water  is  cooled  15  degrees  and  which  gives 
off  150  heat  units  per  square  foot  per  hour.  The  heat  given  off 
equals  100  X  150,  or  15,000  heat  units  per  hour.  Since  the  water 
is  cooled  15  degrees,  each  pound  gives  up  15  heat  units;  therefore, 
looo  pounds  must  be  cooled  in  an  hour.  Suppose  the  water 
enters  at  170  degrees.  Table  XXX,  herewith,  shows  that  water  at 
this  temperature  weighs  60.801  pounds  per  cubic  foot.  Therefore, 
looo  -7-  60.801,  or  16.41  cubic  feet,  must  pass  through  a  100  square 
foot  radiator  to  give  up  the  heat  units  stated.  This  number  of 
cubic  feet  multiplied  by  7^2  gives  the  number  of  gallons  required 
—viz.,  123.1. 


no  Principles    of   Heating. 

TABLE  xxx. 

VOLUME  AND   WEIGHT  OF  DISTILLED  WATER. 

"  Weisbach." 

Tempera-                                        Weight  of  Tempera-                                       Weight  of 

ture  in                                       a  cubic  foot  ture  in                                       a  cubic  foot 

degrees  F.                                     in  pounds,  degrees  F.                                       in  pounds. 

32     62.417  170 60.801 

39.1 62.425  180 60.587 

40 62.423  190 60.366 

50     62.409  200 60.136 

60     62.367  210 59.894 

70     62.302  212 59.707 

80     62.218  220 59.641 

90     62.119  230 59.372 

100     62  240 59.096 

110     61.867  250.  . 58.812 

120     61.720  260 58.517 

130     61.556  270 58.214 

140     61.388  280 57.903 

150     61.204  290 57.585 

160     61.007  300 57.259 

THE   VELOCITY    IN    HOT    WATER    HEATING    PIPES. 

To  compute  the  velocity  in  pipes,  suppose,  for  example,  a 
2-inch  pipe  supplies  200  square  feet  of  surface,  the  water  to  drop 
20  degrees  in  passing  through  the  radiator.  This  amount  of 
surface  will  give  off  about  200  X  150  heat  units  =  30,000  heat 
units  per  hour.  Suppose  the  water  enters  at  170  degrees,  weigh- 
ing 60.801  pounds  per  cubic  foot.  Each  pound  gives  up  20  heat 
units;  then,  30,000  -f-  (60.801  X  20)  24.6  cubic  feet  must  pass 
through  the  radiator  per  hour,  equal  to  about  0.41  cubic  foot  per 
minute.  A  2-inch  pipe  has  an  area  of  0.0233  square  foot,  there- 
fore the  velocity  must  be  about  17.6  feet  per  minute,  or  0.293 
foot  per  second. 

The  velocities  in  the  pipes  of  hot  water  heating  systems  are 
very  low,  as  they  must  be,  for  the  water  to  circulate  with  the  small 
head,  due  to  the  difference  in  temperature  between  the  water  in 
the  flow  and  return  pipes. 

RADIATING  SURFACE   SUPPLIED   BY   PIPES   OF  DIFFERENT   SIZES. 

If  the  volume  of  water  passing  through  pipes  of  different  sizes 
is  known,  the  radiating  surface  they  will  supply  may  be  readily 
computed.  With  the  same  drop  in  temperature  in  radiators,  the 
force  causing  circulation  will  be  alike  in  all.  With  pipes  of  equal 
length  the  resistance  will  vary  as  the  square  of  the  velocity,  and 


Capacities    of    Pipes    for    Hot    Water    Heating.        in 

u-. 
inversely  as  for  the  diameter  expressed,  as— 7- 

Now,  if  we  assume,  for  example,  that  a  2-inch  pipe  will  supply 
200   square   feet   of   direct   radiation — which    in   practice   it   will 

readily  do — and  compute  the  value  of —7-  then  make  —  the  same 

a  a 

for  pipes  of  other  sizes,  a  table  may  be  prepared  showing  the 
radiating  surface  that  may  be  supplied  by  pipes  of  different  diame- 
ters when  working  under  the  same  conditions  with  respect  to  the 
head  causing  the  flow  and  the  resistance  to  the  circulation.  This 
has  been  done,  and  the  results  are  stated  in  the  following  table: 


TABLE  XXXI. 

THE  CAPACITY  OF  MAINS  100  FEET  LONG  EXPRESSED  IN  THE  NUMBER  OF  SQUARE: 
FEET  OF  DIRECT  HOT  WATER  RADIATING  SURFACE  THEY  WILL  SUPPLY  WITH 
THE  OPEN  TANK  SYSTEM,  WHEN  THE  RADIATORS  ARE  PLACED  IN  ROOMS  A'H 
70  DEGREES  F. 


Capacity  in 

Actual 

Nominal 

square  feet 

inside 

Actual 

Capacity 

diameter 

of  direct 

diam- 

inside 

Area  in 

Area  in 

in  gallons 

of  pipes. 

radiating 

eter  i.n 

diameter 

square 

square 

per  foot 

Inches. 

surface. 

inches. 

in  feet. 

inches. 

feet. 

length. 

1% 

75 

1.38 

0.125 

1.49 

0.0104 

0.0777 

1% 

107 

1.61 

0.134 

2.04 

0.0141 

0.1058 

2 

200 

2.07 

0.172 

3.35 

0.0233 

0.1743 

2% 

314 

2.47 

0.206 

4.78 

0.0332 

0.2483 

3 

540 

3.07 

0.256 

7.39 

0.0513 

0.3835 

3y3 

780 

3.55 

0.296 

9.89 

0.0687 

0.5136 

4 

1,060 

4.03 

0.333 

12.73 

0.0884 

0.6613 

4y2 

1,410 

4.50 

0.375 

35.94 

0.1108 

0.829 

5 

1,860 

5.04 

0.417 

19.99 

0.1388 

1.038 

6 

2,960 

6.06 

0.500 

28.89 

0.2006 

1.500 

7 

4,280 

7.02 

0.583 

38.74 

0.2690 

2.012 

8 

5,850 

7.98 

0.666 

50.04 

0.3474 

2.599 

NOTE. — The  above  ratings  in  the  second  column  are  based  on  buildings  hav- 
ing not  more  than  three  floors  above  the  basement.  With  higher  buildings  the 
capacities  would  be  increased. 


It  is  of  some  interest  to  compare  with  Table  XXXI  the  pipe 
capacities  that  have  been  presented  in  various  publications  and 
trade  catalogues.  Table  XXXII  gives  such  a  comparison,  and 
shows  a  wide  variation  in  the  computed  capacities  stated  by  va- 
rious engineers : 


H2  Principles    of    Heating. 

TABLE  XXXII. 

THE    CAPACITY    OF    HOT    WATER    HEATING     MAINS    EXPRESSED     IN    THE    NUMBER    OF 
SQUARE  FEET  OF  DIRECT   RADIATING   SUKFACES    SUPPLIED. 

Diameter 
of  pipe. 


Inches. 

A. 

B. 

c. 

D. 

E. 

F. 

G. 

1 

30 

44 

.... 

30 

.   50 

.... 

89 

1*4 

64 

69 

78 

60 

90 

140 

iMs 

95 

100 

111 

100 

130 

200 

202 

2 

156 

176 

184 

200 

250 

325 

359 

2% 

256 

275 

260 

350 

400 

450 

561 

3 

381 

400 

405 

550 

540 

700 

807 

3% 

531 

540 

576 

850 

740 

900 

1,099 

4 

706 

710 

784      1 

200 

890 

1,200 

1,436 

4y2 

906 

890 

990 

... 

1,100 

1,500 

1,817 

5 

1,131 

1,100 

1,240 

.  .  . 

1,600 

2,000 

2,244 

6 

1,525 

1,600 

1.920 

.... 

3,000 

3,228 

7 

2,150 

2,760 

.... 

4,200 

4,396 

8 

2,750 

....  • 

3,570 

.  .  . 

.... 

5,600 

5,744 

9 

3,625 

.... 

.... 

.  .  . 

.... 

7,268 

10 

4,525 

.... 

6,050 

.... 

8,976 

Authorities. 

A — J.  L.  Bixley  ;  B — J.  H.  Kinealy  ;  C — J.  L.  Mott  Iron  Works  ;  D — C.  L. 
Hubbard  ;  E — R.  C.  Carpenter  ;  F — Model  Heating  Company  ;  G — Nason  Mfg. 
Company. 

PIPE    SIZES    FOR    INDIRECT    HEATING. 

Since  indirect  radiators  are  placed  at  a  much  lower  level,  with 
reference  to  the  heater,  than  are  direct  radiators,  the  head  corre- 
sponding to  the  difference  in  temperature  between  the  supply  and 
the  return  pipes  is  much  less  than  is  the  case  with  the  latter,  and 
scarcely  exceeds  1-20  foot.  Since  cold  air  comes  in  contact  with 
the  radiators,  the  loss  of  heat  per  square  foot  is  much  greater 
than  from  direct  radiators.  These  two  causes  make  it  necessary 
to  provide  much  larger  pipes  to  supply  a  given  amount  of  surface 
than  in  the  case  of  direct  radiators. 

For  supplying  indirect  radiators,  C.  L.  Hubbard  recommends 
using  il/4 -inch  pipes  for  30  square  feet,  i^-inch  for  31  to  50,  2- 
inch  for  51  to  100,  2^-inch  for  101  to  200,  3-inch  for  201  to  300, 
3^ -inch  for  301  to  400,  and  4-inch  for  401  to  600.  Baldwin 
recommends  allowing  a  2-inch  pipe  to  100  square  feet  of  indirect 
radiation.  This  rule  gives  much  larger  pipes  than  customary. 
Certain  hot  water  fitters  use  i%-inch  pipes  to  60  square  feet,  i^- 
inch  for  61  to  120,  and  2-inch  for  121  to  240  square  feet.  With 
pipes  carrying  so  much  radiating  surface  as  the  latter,  the  drop  in 
temperature  of  the  water  in  passing  through  the  radiators  must 


Capacities    of    Pipes    for    Hot    Water    Heating.        113 

be  greater  than  when  larger  pipes  are  used.  The  objection  to 
small  pipes,  with  consequent  increased  drop  in  temperature  to 
overcome  resistance,  is  that  the  mean  temperature  of  the  radiator 
is  lowered,  and  the  heat  given  off  per  square  foot  is  diminished. 
What  is  saved  in  piping  must  be  made  up  in  radiation. 

The  writer  considers  it  unwise  to  supply  more  than  200  square 
feet  of  indirect  radiation  with  a  2-inch  pipe,  and  prefers  rating  a 
2-inch  pipe  to  supply  150  square  feet  of  indirect  surface.  Taking 
the  latter  as  a  basis,  pipes  of  other  sizes  would  supply  the  surface 
stated  in  Table  XXXIII  when  working  against  the  same  resist- 
ance, which  varies  as  the  square  of  the  velocity  and  inversely  as 
the  diameter. 

TABLE  XXXIII. 

THE  CAPACITIES  OF  PIPES  EXPRESSED  IN  THE  NUMBER  OP  SQUARE  FEET 
OF  INDIRECT  HOT  WATER  RADIATING  SURFACE  THEY  WILL  SUPPLY  WITH  THK 
OPEN  TANK  SYSTEM. 


Diameter 
of  pipes. 
Inches. 
1V4  

Indirect 
radiating 
surface. 
Square  feet. 
.   56 

Diameter 
of  pipes. 
Inches. 
4 

Indirect 
radiating 
surface. 
Square  feet. 
790 

1%.  .  . 

80 

4y> 

1  060 

f> 

150 

5 

1  400 

2Vo 

035 

6 

2  220 

3 

405 

3  °00 

3i/2.  . 

.  .  585 

8     . 

..4.400 

SIZES  OF  RISERS. 

The  capacities  of  risers  recommended  by  different  writers  are 
as  follows : 

TABLE  XXXIV. 

COMPARISON  OF   RATINGS   FOR   HOT   WATER    RISERS. 

(Hight  of  floors  approximately  10  feet  each.) 
Sizes 

of  pipes.  , First-floor  risers. ^     , Second-floor  risers. N 

in  inches.                              Square  feet  direct  radiation.  Square  feet  direct  radiation. 

% 27        ...              50  ...           35        ...  52 

1     39             48          30             89  45          62          55  92 

1% 64      75    60     140  73    97    90  144 

1% 95     108   100     202  110   140   140  209 

2  156     191   200     359  179   250   275  370 

2i/2 256     300   350     561  294   390   475  577 

3  381     430   550     807     438    835 

3% 531     590   850   1,099     610    1,132 

4 ..  706     770    ...    1,436     812    1,478 

4y2 906     970    ...    1,817   1,042    1,871 

5  1,131   1,200    .  .  .    2,244   1,301    2,309 

6  1,125   1,700    .  .  .    3,228   1,753    3,341 


XI4  Principles    of    Heating. 


f Third-floor  risers. N     , Fourth-floor  risers. ^ 

Square  feet  direct  radiation.      Square  feet  direct  radiation. 


%  

35 

53 

55 

1   ....  

48 

62 

65 

95 

52        ... 

75 

98 

1%  

79 

97 

110 

149 

85 

125 

153 

1%  

118 

140 

165 

214 

126 

185 

222 

2     

194 

250 

375 

380 

206 

425 

393 

2%  

318 

390 

595 

338 

613 

3     

473 

.  . 

856 

503 

888 

sya  

659 

1,166 

701 

1,202 

4     

876 

1,520 

932 

1,571 

4%  

1,124 

1,927 

1,196 

1,988 

5     

1,402 

2,376 

1,493 

.  .  . 

2,454 

6 

1,891 

3,424 

2,013 

3,552 

The  figures  stated  in  the  first,  second,  third  and  fourth  columns,  giving  ca- 
pacities, are  by  Bixley,  Kinealy,  Hubbard  and  Nason,  respectively.  It  will  be 
noted  that  here,  as  in  the  case  of  mains,  the  capacities  given  by  the  Nason  Com- 
pany are  much  in  excess  of  others.  The  figures  given  by  Prof.  Kinealy  are  based 
on  water  at  high  temperature  and  may  be  increased  25  per  cent,  for  water  at 
160  degrees  in  the  radiator. 

The  following  table  has  been  compiled  by  the  writer,  using  as 
a  basis  a  1^2 -inch  pipe  rated  to  supply  100  square  feet  of  direct 
radiation  on  the  first  floor,  140  square  feet  on  the  second,  175 
square  feet  on  the  third  and  200  square  feet  on  the  fourth.  The 
capacities  of  other  pipes  are  based  on  a  flow  that  represents  the 
same  resistance  to  be  overcome  as  in  the  i^-inch  pipes,  as  above 
rated;  that  is,  the  capacities  of  pipes  larger  than  i^-inch  are 
based  on  a  higher  velocity  and  smaller  pipes  on  a  correspondingly 
lower  velocity,  since  the  resistance  varies  directly  as  the  square  of 
the  velocity  and  inversely  as  the  diameter. 

TABLE  XXXV. 

THE  CAPACITIES  OF  RISERS  EXPRESSED  IN  THE  NUMBER  OF  SQUARE  FEET 
OF  DIRECT  HOT  WATER  RADIATING  SURFACE  THEY  WILL  SUPPLY  ON  DIFFER- 
ENT FLOORS. FLOOR  HIGHTS  APPROXIMATELY  10  FEET. OPEN  TANK  SYSTEM. 

RADIATORS    IN   ROOMS  AT   70   DEGREES   F. 

Diameter 

of  riser.  f — Square  feet  of  direct  radiating  surface  supplied. — ^ 

in  inches.  First  floor.     Second  floor.     Third  floor.     Fourth  floor. 

1     33  46  57  64 

1%, 71  104  124  142 

iy2 100  140  175  200 

2     187  262  325  375 

2% 292         410         492         580 

Z  500         755         875        1,000 

RADIATOR  CONNECTIONS. 

Direct  hot  water  radiators  are  commonly  tapped  I  inch  up  to 
40  square  feet,  i%  inches  for  41  to  72  square  feet,  and  il/2  inches 
for  ordinary  sizes  larger  than  72  square  feet. 


Capacities    of    Pipes    for    Hot    Water    Heating.        115 

ELBOWS  AND  BENDS. 

The  resistance  interposed  by  elbows  to  the  passage  of  water  is 
a  subject  on  which  there  appears  to  be  little  available  data  of 
value.  Fortunately,  it  is  unnecessary,  in  ordinary  heating  work, 
to  compute  the  loss  of  heat  due  to  this  resistance.  The  writer,  in 
a  series  of  articles  on  the  flow  of  steam,  gives  a  table  showing 
the  lengths  of  straight  pipe  that  would  present  the  same  resistance 
as  a  standard  elbow.  The  values  there  given  will  be  found  con- 
venient for  use  in  case  it  is  desired  to  allow  for  the  resistance  of 
elbows  in  an  extensive  system  of  hot  water  heating. 

In  the  smaller  sizes  of  fittings,  say  from  \}/2  to  4  inches,  the 
radius  of  the  center  line  of  the  elbow  is  roughly  1^4  x  the  diameter 
of  pipe  for  standard  elbows;  1^4  x  the  diameter  of  pipe  for  the 
long  turn  patterns  and  2^4  x  the  diameter  of  pipe  for  extra  long 
turn  elbows.  The  relative  resistance,  or  loss  of  head,  computed 
from  Weisbach's  formula  is,  for  these  three  patterns,  as  follows : 
Standard,  100 ;  long  turn,  83 ;  extra  long  turn,  77.  While  these 
figures  may  be  considered  merely  approximate,  they  serve  to  show 
in  a  general  way  the  great  advantage  of  long  turn  elbows  over 
those  of  standard  patterns  for  hot  water  work. 

Ordinary  wrought  iron  or  steel  pipe  bends  have  a  radius  of 
axis  equal  to,  at  least,  5  x  the  diameter  of  pipe.  With  such  bends, 
Trautwine  states,  the  flow  will  not  be  materially  diminished.  In 
first-class  hot  water  heating  plants  long  turn  elbows  are  used,  and 
the  ends  of  the  pipes  are  reamed  inside  to  reduce,  as  far  as  possi- 
ble, the  resistance  to  the  flow  of  water  and  to  permit  the  least 
difference  possible  between  the  temperature  in  the  supply  and 
return  pipes. 

EXPANSION  TANKS. 

Hot  water  expands  about  4  per  cent,  of  its  volume  at  40 
degrees  when  heated  to  200  degrees.  Taking  these  as  the  ex- 
tremes of  temperature  between  the  water  when  the  system  is  first 
filled  and  when  operating  in  coldest  weather,  and  assuming  that 
the  expansion  tank  should  have  a  capacity  equal  to  twice  this 
increase  in  volume,  the  tank  should  be  made  8  per  cent.,  or  about 
one-twelfth,  of  the  total  volume  of  radiator  and  piping.  Sup- 
pose the  piping  is  equivalent  to  one-third  the  direct  radiating  stir- 


Il6  Principles    of   Heating. 

face  and  the  volume  of  water  in  the  system  to  amount  to  i^ 
pints  per  square  foot  of  radiating  surface,  including  mains,  then, 
for  example,  a  lo-galion  expansion  tank  would  be,  adapted  to  a 
system  holding  120  gallons,  which,  on  the  basis  of  iy2  pints  per 
square  foot  of  radiation,  mains  included,  would  be  640  square 
feet.  And,  since  mains  are  reckoned  at  one-third  the  actual  sur- 
face in  radiation,  the  latter  would  amount  to  three-fourths  of 
640  square  feet  equal  480  square  feet,  or,  say,  in  round  numbers, 
500  square  feet.  On  the  same  basis  the  capacity  of  other  tanks 
would  be  in  proportion,  as  follows : 

TABLE  XXXVI. 

CAPACITY   OF   EXPANSION    TANKS. 

Capacity    in    square    feet    of 

Capacity  actual  surface  in  hot  water 

of  tank  radiator  to  which  tank  is 

in  gallons.  adapted. 

5  250 

10  500 

15  750 

20  1,000 

30  1,500 

40  2,000 

50  2,500 

60  3,000 

It  will  be  noted  that  the  capacities  in  the  above  table  are 
equivalent  to  I  gallon  in  expansion  tank  to  each  50  square  feet 
of  surface  in  radiators;  a  convenient  rule.  While  tanks  may  be 
made  smaller,  the  saving  would  be  slight,  and  they  would  require 
more  frequent  attention,  unless  fitted  with  an  automatic  water 
line  regulator. 

It  is  beyond  the  scope  of  this  work  to  discuss  methods  of  pip- 
ing; yet  the  writer  feels  constrained  to  warn  fitters  against  the 
danger  in  placing  a  valve  in  the  expansion  pipe,  which  is  some- 
times done,  and  also  to  see  to  it  that  the  expansion  pipe  and  tank 
are  located  where  there  will  be  no  danger  from  freezing. 


CHAPTER  XL 
VACUUM  AND  VAPOR  SYSTEMS  OF  STEAM  HEATING. 

This  chapter  is  made  up  chiefly  of  articles  that  appeared  in 
The  Metal  Worker  during  the  year  1906  under  the  heading, 
"  Modified  Systems  in  Steam  Heating,"  by  "  Progress."  These 
articles  have  been  revised  and  supplemented  by  others  relating 
to  systems  that  properly  come  under  this  heading. 

THE  WEBSTER  SYSTEM. 

In  the  Webster  system  of  steam  circulation  the  steam  supply 
to  the  radiators  is  controlled  by  a  hand  wheel  valve  as  in  the  or- 
dinary two-pipe  system.  At  the  return  end  of  each  radiator  is 
placed  a  so-called  "  thermo-valve,"  Fig.  34,  or  a  water  seal  motor, 
Fig.  35,  either  of  which  allows  the  escape  of  air  and  water  and 
prevents  the  escape  of  steam.  Since  air  is  heavier  than  saturated 
steam,  in  the  ratio  of  i  to  ^  at  atmospheric  pressure,  the  loca- 
tion of  the  thermo-valve  at  the  lower  end  of  the  radiator  oppo- 
'site  the  steam  inlet  is  stated  to  be  the  most  effective  one  possible. 
Air  valves  are  not  required  with  the  Webster  system.  Typical 
radiator  connections  are  shown  in  Fig.  36.  It  is  essential  that 
each  unit  of  radiation  be  equipped  with  one  of  the  valves  des- 
cribed, or  one  performing  the  same  functions,  otherwise  any  unit 
without  one  would  permit  steam  to  pass  into  the  returns  and  de- 
stroy the  vacuum  which  it  is  the  function  of  the  pump  to  maintain. 
By  means  of  this  suction  a  continuous  removal  of  condensation 
and  air  from  the  heating  system  is  secured. 

The  water  drawn  from  the  system  is  discharged  by  the 
vacuum  pump  to  a  feed  water  heater,  any  air  in  the  system  es- 
caping from  an  air  separating  chamber  provided  on  the  discharge 
line  between  the  pump  and  the  heater.  (See  Fig.  37.)  The  feed 
water  heaters  are  commonly  connected  with  a  branch  exhaust  pipe, 
this  method  of  piping  being  preferred  by  the  patentees  of  the  sys- 
tem to  passing  all  the  exhaust  steam  from  the  engines  through 
the  heater. 

The  vacuum  pump  exerts  a  suction  on  the  return  ranging  as 

117 


n8  *          Principles    of    Heating. 

a  rule  from  4  to  15  inches  mercury  column,  according  to  the 
length  and  size  of  the  pipes.  With  this  system  high  pressure 
returns  must  not  be  connected  with  the  returns  leading  to  the 
vacuum  pump,  since  the  high  temperature  of  the  condensation 
causes  the  water  to  vaporize  in  the  returns  and  interferes  with  the 


•    ...  . 


Fig.  34.—  Sectional  View  Webster  Water  Seal  Motor. 

maintenance  of  the  vacuum.     The   exhaust   from   the   pump   is 
utilized  in  the  heating  system. 

HEATING   AT    NIGHT. 

In  buildings  heated  by  this  system  it  is  possible  to  supply  an 
amount  of  live  steam  less  than  that  required  to  completely  fill  the 
system  at  atmospheric  pressure,  hence  a  saving  may  be  made  by- 
heating  at  night  with  steam  at  a  pressure  below  that  of  the  at- 
mosphere. 

It  is  often  desirable  to  locate  some  radiating  surface  at  a  point 
lower  than  the  main  return.  With  the  Webster  system  the  con- 
densation may  be  raised  several  feet  above  the  level  of  the  radi- 
ator to  be  drained  bv  reason  of  the  suction  in  the  returns. 


Vacuum  and  Vapor  Systems  of  Steam  Heating.         i  ig 

BACK  PRESSURE  VALVES    AND  PRESSURE   REDUCING  VALVES. 

The  back  pressure  and  pressure  reducing  valves  need  not  be 
set  to  produce  initial  pressure  in  the  heating  mains  in  excess  of 
that  required  to  supply  the  most  remote  unit  of  radiation  with 
steam  at  atmospheric  pressure.  The  initial  pressure  may  be 


Fig.  35. — Exterior  View  Webster  Water  Seal   Motor. 

varied  according  to  the  outside  temperature,  as  required.  On 
high  pressure  jobs  two  reducing  valves,  set  tandem,  are  sometimes 
installed,  the  first  to  reduce  from  boiler  pressure  down  to  15  or 
20  pounds,  the  latter  to  reduce  to  atmospheric  pressure  or  a  few 
ounces  above. 

ADVANTAGES    CLAIMED. 

The  Webster  Company  in  its  publications  sets  forth  these  ad- 
vantages : 

i.  Absence  of  back  pressure  on  motive  engines  when  exhaust 
steam  is  utilized. 


120  Principles   of   Heating. 

2.  A  perfect  drainage  of  supply  pipe  systems  preliminary  to 
an  equally  perfect  drainage  of  radiating  surface  without  the  loss 
of  steam. 

3.  A  continuous  automatic  drainage  of  condensation  and  the 
prevention  of  any  accumulations  of  water. 

4.  A  positive  and  consequently  effective  steam  circulation. 

5.  Perfect  control  of  circulation  with  power  to  vary  it  at  will 


THERMO  VALVE 

OR  WATER 
SEAL   MOTOR 


Fig.  36. — Typical  Radiator  Connections. 

6.  Removal  of  air  and  gases  from  heating  surfaces  and  feed 
water. 

7.  Power  to  independently  modulate  temperature  in  any  part 
of  the  heating  surface. 

8.  The  return  of  condensation  from  points  somewhat  below 
the  line  of  drip  or  drainage  mains  when  necessary. 

9.  Smaller  pipes  may  be  used  than  with  the  ordinary  low  pres- 
sure two-pipe  system. 

It  is  pointed  out  that  the  positive  removal  of  air  from  the  radi- 
ators.is  alone  a  great  advantage,  since  automatic  air  valves  seldom 
properly  perform  the  function  for  which  they  were  designed,  and 
unless  air  lines  lead  from  them  to  some  suitable  point  of  discharge 
the  ill-smelling  air  from  the  radiators  is  discharged  into  occupied 
rooms. 

Water  hammer,  due  to  ignorance  or  carelessness  in  operating 
radiator  valves,  is  entirely  overcome  by  the  use  of  the  two-pipe 
vacuum  system.  The  supply  valve  is  the  only  one  that  requires 
any  attention,  the  return  being  automatic.  The  supply  of  steam 
may  be  throttled  down  at  will,  and  the  vacuum  maintained  on 


OUCHAROE  TO  neccrvmo 


Fig.  37.— Typical  Arrangement  of  Vacuum  Pump  and  Feed  Water  Heater  In  Webster  Vacuum  Heating  System, 


121 


122  Principles    of    Heating. 

the  returns  causes  the  continuous  removal  of  condensation  from 
the  radiators  and  prevents  any  backing  up  of  water. 

The  steam  pressure  in  the  radiators  is  not  reduced  by  the 
vacuum  maintained  on  the  return,  but  depends  solely  on  the 
amount  of  steam  admitted  to  the  radiators.  Indirectly  the  vac- 
uum on  the  return  affects  the  steam  pressure,  since  no  pressure 
whatever  above  the  atmosphere  is  required  in  the  radiators  for 
the  purpose  of  forcing  the  water  of  condensation  through  them 
and  the  air  out  of  them.  In  the  case  of  old  plants  having  insuffi- 
cient radiation  for  the  most-  severe  weather,  when  using  the  very 
low  pressures  common  with  vacuum  systems  it  is  often  better  pol- 
icy to  carry  a  few  pounds  back  pressure  on  the  engines  furnish- 
ing the  exhaust  steam  during  such  weather  than  to  overhaul  the 
entire  heating  system. 

This  system  secures  the  ready  circulation  of  steam  through- 
out buildings  widely  separated,  and  that,  too,  with  only  a  slight 
back  pressure  on  the  engines.  With  the  usual  methods  of  steam 
heating  it  is  necessary  to  carry  a  back  pressure,  even  during  mild 
weather,  when  the  full  efficiency  of  the  radiating  surfaces  is  not 
required,  and  when  but  few  of  the  radiators  of  an  extensive  sys 
tern  may  be  needed.  Under  certain  conditions  it  would  be  cheaper 
to  supply  live  steam  at  reduced  pressure  than  to  carry  back  pres- 
sure on  the  engines  in  order  to  supply  a  small  amount  of  radiating 
surface. 

PIPE  SIZES. 

Since  with  this  system  no  pressure  is  necessary  in  the  radi- 
ators to  force  out  the  air  and  water,  it  follows  that  a  drop  in  pres- 
sure of  only  a  few  ounces  from  the  initial  pressure  will  be  suffi- 
cient to  cause  the  necessary  flow  of  steam  through  the  pipes. 

These  may  be  made  smaller  than  is  customary  with  the  ordi- 
nary two^-pipe  low  pressure  system,  and  the  returns  may  be  decid- 
edly cut  down  in  size  owing  to  the  action  of  the  vacuum  pump 
creating  a  rapid  flow  in  them.  See  pipe  sizes,  pages  92  and  93. 
The  supply  pipes  may  be  made  one  or  two  sizes  smaller  with  the 
vacuum  system,  and  the  returns  two  to  three  sizes  smaller  than 
would  be  used  with  the  ordinary  low  pressure  system. 


Vacuum  and  Vapor  Systems  of  Steam  Heating.        123 

THE  PAUL  SYSTEM. 

The  Paul  system  secures  the  removal  of  air  from  radiators 
through  air  valves  of  the  expansible  plug  type  connected  with 
air  lines  leading  to  a  steam  ejector.  See  Fig.  38.  It  may  be  ap- 
plied either  to  one-pipe  or  two-pipe  systems  (see  Figs.  39  and 
40),  the  water  returning  in  the  same  manner  as  in  ordinary  low 


AIR  Line) 


Fig.  38.— Front  Elevation  of  Paul  Exhausting  Apparatus. 

pressure  steam  heating  plants.  This  system  handles  the  air  alone, 
whereas  the  Webster  system  removes  both  the  air  and  condensa- 
tion from  radiators. 

That  air  is  the  most  serious  hindrance  to  the  proper  opera- 
tion of  a  steam  heating  plant  is  a  well-known  fact.  To  attempt 
to  get  rid  of  it  by  forcing  it  through  ordinary  automatic  air  valves 
by  steam  pressure  is  a  rather  slow  process,  especially  in  the  case 
of  large  coils  or  radiators.  With  a  common  low  pressure  system 
the  air  remains  in  the  radiators  until  forced  out  by  the  steam. 
With  the  vacuum  system  the  air  may  be  removed  from  the  radia- 


124 


Principles    of   Heating. 


tors  by  starting  the  ejector  before  steam  is  turned  on  the  system. 
The  radiators  then  become  quickly  rilled  with,  and  remain  full  of, 


£L-AIR  VACVE 

i 


-X" 


TO  EJECTOR^ 

Fig.  39. — Paul  System  Connections  for  One-Pipe  System 

/T\/r\/T\/r\/t\/T\/T\/r\/T\/t\ 


AIR  VALVE 


Fig.  40.— Paul  System  Connections  for  Two-Pipe  System. 


steam,  since  the  air  is  automatically  removed  as  rapidly  as  ii 
accumulates. 


Vacuum  and   Vapor  Systems  of  Steam  Heating.         125 

ABSENCE   OF    BACK    PRESSURE. 

One  of  the  chief  advantages  of  this  system  over  ordinary  low 
pressure  heating  is  the  removal  of  back  pressure  from  the  engines 
and  pumps.  This  is  especially  important  in  modern  city  build- 
ings, where  this  system  finds  its  widest  application.  By  exhaust- 
ing the  air  from  the  radiators  by  means  of  the  steam  ejector  they 
become  practically  condensers,  the  engines  exhausting  into  them, 
or,  in  other  words,  the  radiators  draw  steam  from  the  engines 
to  them,  due  to  the  rapid  condensation  which  they  are  capable  of 
producing.  In  manufacturing  plants  where  the  power  require- 
ments may  be  in  excess  of  those  for  heating  the  importance  of 
the  elimination  of  back  pressure  is  apparent. 

STEAM   TO  OPERATE  THE  EJECTOR. 

As  to  the  amount  of  live  steam  required  to  operate  the  ejector, 
it  is  claimed  this  amounts  to  but  little  if  the  plant  is  properly  op- 
erated, since  after  the  system  has  once  been  cleared  of  air  it  ac- 
cumulates slowly  and  may  be  removed  with  the  expenditure  of 
a  small  volume  of  live  steam. 

To  compute  the  volume  of  steam  escaping  from  an  orifice  to 
the  atmosphere,  allow  about  900  feet  velocity  per  second  and  mul- 
tiply by  the  area  of  the  opening  expressed  in  the  decimal  part  of 
a  square  foot.  As  to  the  amount  of  steam  required  to  operate 
the  ejector,  A.  B.  Franklin  in  a  paper  on  the  Paul  system  of  ex- 
haust steam  heating,  read  before  the  Master  Steam  and  Hot 
Water  Fitters'  Association  of  the  United  States,  June  7$  1893, 
states  that  in  ten  hours'  run,  with  a  fan  system  of  heating  having 
heaters  containing  an  aggregate  of  24,150  linear  feet  of  i^-inch 
pipe,  supplied  by  a  6-inch  main,  the  ejector  discharging  to  a  con- 
denser used  300  pounds  of  steam  in  that  length  of  time.  A  test 
made  at  the  Ohio  State  University  showed  the  total  weight  of 
water  returned,  from  the  radiators  to  be  8160  pounds  and  the 
steam  used  by  the  exhauster  or  ejector  to  be  432  pounds. 

ADVANTAGES  CLAIMED. 

Claims  for  the  Paul  system  are : 

1.  A  positive  and  uniform  circulation  of  steam  without  pres- 
sure above  that  of  the  atmosphere. 

2.  Utilizing  the  heat  of  steam  at  low  temperatures,  thereby 
gaining  great  economy. 


126  Principles    of    Heating. 

.  3.  Warming  without  impairing  the  quality  of  the  air  in  the 
rooms. 

4.  The  independent   and  automatic   removal   of  the   air  and 
water  of  condensation  from  the  heating  apparatus. 

5.  A  sealed  system ;  no  leakage,  no  smell  or  dripping  from  air 
valves. 

6.  All  heating  surface  held  in  the  best  condition  to  operate 
promptly  when  desired,  and  all  parts  of  the  surface   rendered 
uniformly  efficient  when  steam  is  turned  on. 

7.  Exhaust   steam  utilized  without  back  pressure  at  engine 
or  pumps. 

8.  The  water  of  condensation  returned  quickly  and  econom- 
ically at  highest  temperatures. 

9.  Less  steam  used,  less  coal  burned,  to  heat  a  given  space. 

HEATING   WITH    RADIATORS    AT   A    RELATIVELY    LOW   TEMPERATURE. 

Professor  Kinealy,  reporting  on  some  tests  to  show  the  effect 
of  the  relatively  low  temperatures  secured  by  the  use  of  a  vacuum 
system,  makes  the- following  statement:  "The  radiator  at  high 
temperature  probably  kept  the  air  at  the  top  of  the  room,  when 
the  temperature  about  5  feet  from  the  floor  was  70  degrees,  at 
a  much  higher  temperature  than  it  was  kept  when  the  temperature 
in  the  radiator  was  low.  The  higher  the  temperature  of  the  air 
at  the  ceiling  of  the  room  the  greater  will  be  the  average  tem- 
perature of  the  air  in  contact  with  the  cooling  windows  and  walls 
of  the'  building,  and  therefore  for  a  given  outside  temperature 
the  greater  will  be  the  difference  between  the  average  temperature 
of  the  air  inside  and  that  of  the  air  outside,  and  hence  the  greater 
will  be  the  amount  of  heat  transmitted  through  the  cooling  walls 
and  windows  per  hour.  As  the  occupants  of  heated  rooms  live 
in  the  air  which  is  within  6  feet  of  the  floor,  that  system  of  heat- 
ing must  undoubtedly  be  the  best  and  the  most  economical  which 
will  maintain  the  desired  temperature  of  the  room  nearly  uniform 
from  the  floor  to  5  feet  above  it,  with  a  low  temperature  in  the 
upper  part  of  the  room,  and  this  is,  I  think,  done  by  radiators  sup- 
plied with  steam  at  low  temperatures."  (See  "Heating  with 
Steam  at  or  Below  Atmospheric  Pressure,"  by  J.  H.  Kinealy,  in 
The  Metal  Worker,  Plumber  and  Steam  Fitter,  July  29,  1899). 


Vacuum  and  Vapor  Systems  of  Steam  Heating.         127 

DONNELLY    POSITIVE    DIFFERENTIAL    SYSTEM    OF    EXHAUST    STEAM 

CIRCULATION. 

In  this  system  a  controlling  valve  (see  Fig.  41)  is  placed  at 
the  foot  of  return  risers  as  indicated  in  Fig.  43.  These  valves  are 
designed  to  maintain  any  desired  difference  in  pressure  between 


I      T 

Fig.  41. — Differential  Pressure  Controlling  Valve, 
f 


Fig.  42. — Impulse  Automatic  Valve. 

the  supply  and  return  risers.  By  maintaining  this  constant  pres- 
sure difference  it  is  claimed  that  a  special  type  of  valve  of  simple 
design  may  be  used  at  the  radiator.  A  small  opening  is  provided 
for  the  removal  of  air  when  this  valve  is  closed.  When  open, 
both  air  and  water  pass  through  it.  Valves  of  other  patterns 
are  used,  but  the  impulse  valve,  so  called,  shown  in  Fig.  42,  serves 
to  illustrate  their  use.  It  is  claimed  that  dirt  and  scale  will  freely 
pass  through  these  valves. 

Fig.  43  illustrates  the  application  of  this  system  to  coils.   The 
main  supply  riser  is  drained  through  a  siphon  loop  to  the  return. 


128 


Principles    of   Heating. 


It  is  claimed,  since  all  return  risers  may  be  kept  in  the  same  con- 
dition by  means  of  the  controlling  valve,  that  the  valve  illustrated 
in  Fig.  42  requires  little  or  no  adjustment  and  that  all  air  and 
condensation  is  drawn  away  from  the  radiating  surfaces  to  the 


Fig.  43. — Application  of  the  Donnelly  System  to  Radiating  Coils. 

vacuum  pump.    It  is  further  claimed  that  no  short  circuiting  can 
occur. 

THE  THERMOGRADE  SYSTEM   OF  STEAM    HEATING. 

The  Thermograde  system  of  low  pressure  steam  heating  pro- 
vides for  the  control  of  the  heat  emitted  by  radiators  by  regulating 
the  admission  of  steam  to  them.  A  control  valve,  illustrated  in  Fig. 
44,  is  connected  with  the  inlet  of  each  radiator.  These  valves  are 
intended  to  be  capable  of  adjustment  to  admit  enough  steam  to 
fill  one-quarter,  one-half,  three-quarters  or  a  fractional  part  of 
the  radiator.  When  the  handle  is  turned  a  lug  rides  up  on  a  cam 
and  raises  the  disk  from  the  seat. 


Vacuum  and  Vapor  Systems  of  Steam  Heating.        129 

At  the  return  end  of  each  radiator  is  placed  a  combined  air 
valve  and  expansion  trap.  This  so-called  auto  valve  is  designed 
to  allow  water  and  air  to  escape  from  the  radiator  but  to  prevent 
the  escape  of  steam.  This  valve  is  operated  by  a  liquid  sealed  in 
a  copper  receptacle.  When  steam  comes  in  contact  with  it  the 


Fig.   44. — The  Thermograde  Control  Valve. 

liquid  is  vaporized  and  creates  a  pressure  sufficient  to  force  the 
valve  disk  against  the  seat.  When  the  liquid  cools,  the  valve  is 
opened  by  a  spring. 

Fig.  45  shows  a  radiator  equipped  with  the  supply  and  return 
valves  just  described.  With  this  system  radiators  of  the  hot  water 
type  are  preferable  to  those  of  the  ordinary  steam  pattern,  as  the 
control  valve  may  be  more  conveniently  located  and  because  the 


130  Principles   of   Heating. 

circulation  in  the  radiator  is  said  to  be  somewhat  better  than  with 
steam  radiators. 

When  a  control  valve  is  partially  closed  the  steam  is  con- 
densed in  the  upper  portion  of  the  radiator,  the  lower  portion  is 
cold  and  becomes  filled  with  air  that  backs  up  through  the  return 
valve  or  trap,  the  return  risers  being  open  to  the  atmosphere  at 
the  top  and  free  from  pressure. 

When  the  water  of  condensation  is  returned  to  a  low  pressure 
boiler  it  must  be  permitted  to  back  up  the  main  return  sufficiently 


Fig.  45. — Radiator  Equipped  with  Thermograde  Valves. 

to  overcome  the  boiler  pressure  acting  on  the  end  of  the  return, 
where  it  connects  with  the  boiler. 

The  lowest  radiator  should  be  not  less  than  6  feet  above  the  water 
line  of  the  boiler.  Since  I  pound  pressure  is  equal  to  about  2.3 
feet,  less  than  3  pounds  boiler  pressure  could  be  carried  under 
these  conditions  without  flooding  the  radiators.  The  use  of  a  re- 
turn tank  is  recommended  for  large  jobs.  When  the  condensa- 
tion is  returned  to  a  tank,  as  in  large  buildings,  the  tank  must  be 
vented  to  the  atmosphere. 

The  piping  of  a  Thermograde  system  is  practically  the  same 
as  a  regular  two-pipe  system  except  that  the  returns  must  be  open 
to  the  atmosphere.  The  main  returns  are  generally  run  dry.  The 
company  controlling  this  system  recommends  these  sizes  for 
radiator  connections : 


Vacuum  and  Vapor  Systems  of  Steam  Heating.         131 

TABLE   XXXVII. 

TABLE    OF    SIZES    OF    RADIATOR    CONNECTIONS. THERMOGRADE    SYSTEM. 

Run-outs  from  risers 

to  radiators. 

Radiator  surface.  Control  valve.     Drain  valve.         Supply.         Return. 

Square  feet.  Inch.  Inch.  Inch.  Inch. 

0    to     20 1/2  %  %  % 

21    to      50 %  %  1  % 

51    to   100 1  %  114  1 

100    to    150 11^  %  1%  1 

Advantages  claimed  for  this  system  are : 

1.  Positive  circulation,  due  to  absence  of  pressure  at  the  re- 
turn end  of  the  radiators. 

2.  Quietness  of  operation. 

3.  Control  of  each  unit  of  radiation  independent  of  others. 

4.  Absence  of  separate  air  valves  and  lines,  these  being  com- 
bined with  the  return  carrying  the  water  of  condensation. 

5.  Convenience   in   operation,  there  being  but   one   valve   to 
manipulate. 

6.  Saving  in  fuel,  due  to  absence  of  overheating  in  rooms,  the 
heating  being  more  easily  controlled  than  with  ordinary  steam 
heating  systems. 

7.  The  quick  heating  of  radiators,  due  to  the  rapid  expulsion 
of  air,  there  being  no  steam  pressure  in  the  returns  to  be  over- 
come. 

8.  The  drop  in  pressure  between  the  supply  and  return  lines 
being  greater  than  in  the  ordinary  two-pipe  system,   somewhat 
smaller  pipes  may  be  used  if  necessary. 

M'GONAGLE  VACUUM  SYSTEM  FOR  LOW  PRESSURE  PLANTS. 

The  McGonagle  vacuum  system  provides  for  an  automatic  air 
valve  attached  to  each  radiator,  and  is  described  about  as  follows  in 
the  publications  of  the  company  handling  it :  To  these  air  valves  a 
system  of  air  piping  is  attached.  This  system  of  air  piping  termi- 
nates in  a  special  trap  placed  above  the  water  line  of  the  boiler.  The 
discharge  from  this  trap  is  connected  to  a  return  connection  of  the 
boiler.  A  connection  is  taken  from  a  convenient  point  in  the  air 
line  above  the  trap  and  connected  to  the  combustion  chamber  of 
the  boiler  furnace.  This  pipe  is  supplied  with  a  check  valve  open- 
ing toward  the  furnace.  When  steam  is  generated  in  the  boiler 
it  rises  through  the  steam  pipes  to  the  radiators.  When  the  circu- 


132 


Principles    of    Heating. 


lation  is  established  the  automatic  air  valves  close.     These,  how- 
ever, are  so  adjusted  that  they  will  always  pass  sufficient  steam 


Fig.  46. — Typical  Arrangement  of  the  McGonagle  Vacuum  Heating  System. 

to  keep  the  air  pipe  warm  for  a  distance  of  from  18  inches  to  2 
feet  beyond  the  air  valve. 

When  the  pressure  in  the  air  lines  drops  below  the  barometer 


Vacuum  and  Vapor  Systems  of  Steam  Heating.         133 

pressure  in  the  combustion  chamber  of  the  boiler  the  check  valve 
in  the  pipe  to  the  furnace  closes,  thus  preventing  a  back  flow  of 
the  gases  from  the  furnace  into  the  air  lines.  The  regulation  of 
the  fire  can  be  accomplished  either  by  hand,  in  the  same  manner 
that  a  stove  is  regulated,  or  by  the  use  of  a  special  draft  con- 
troller. 

The  accompanying  diagram  illustrates  the  method  of  installing 
the  McGonagle  system.  The  system  is  shown  as  applied  to  an 
ordinary  one  pipe  job.  The  feature  of  the  system  is  the  arrange- 
ment of  the  air  piping.  If  it  is  desired  to  apply  the  system  to 
two-pipe  work  or  to  another  form  of  one-pipe  work,  the  arrange- 
ment of  the  air  piping  should  remain  the  same  as  shown. 

The  several  parts  of  the  system  are  designated  by  the  follow- 
ing letters  on  the  cut : 

A.  Air  valves  of  special  design. 

B.  Boiler. 

C.  Connection  to  furnace. 

D.  Discharge  of  trap. 
M.  Air  pipe. 

R.  Radiators. 

T.  Trap  of  special  design. 

V.  Check  valve. 

S.  Steam  pipe. 

P.  Pressure  gauge. 

G.  Vacuum  gauge. 

N.  Safety  valve. 

SUGGESTIONS  TO   FITTERS. 

The  radiation  intended  to  heat  the  rooms  should  be  figured 
on  the  same  basis  that  would  be  used  in  apportioning  radiation 
for  any  first-class  job  which  was  intended  to  heat  with  2  or  3 
pounds  pressure.  The  same  size  piping  should  be  used  and  the 
same  care  exercised  in  draining  and  dripping  the  pipe  that  would 
be  necessary'  if  it  were  intended  to  erect  the  apparatus  without 
the  use  of  the  vacuum  system.  Extra  precaution  should  be  taken, 
however,  to  have  all  joints  tight,  and  to  have  all  fittings  free  from 
sand  holes. 

Care  should  be  taken  that  all  valves  used  are  carefully  packed 
so  as  to  avoid  the  leakage  of  air  into  the  system  while  the  vacuum 
is  being  maintained.  The  manufacturers'  packing  in  the  valves 
should  not  be  depended  on  but  should  be  removed  and  carefully 
replaced  with  lamp  wick  dipped  in  oil  and  plumbago,  being  sure 


134 


Principles    of    Heating. 


that  sufficient  wick  is  used  to  make  the  valve  tight  around  the 
stem.  All  check  valves  used  should  be  swing  checks,  with  as- 
bestos or  Jenkins'  seats.  Care  should  be  taken  to  see  that  tbere 
is  no  leak  of  air  into  the  system  through  the  safety 
valve,  water  glass,  gauge  cocks  or  other  trim- 
mings. 

The  air  pipe  should  not  be  less  than  *4  mcn  be- 
tween the  air  valve  and  the  first  fitting,  where  it 
should  increase  to  l/2  inch  pipe.  The  first  fitting 
below  the  air  valve  should  therefore  be  a  J4  x  /<2 
inch  elbow  in  every  case.  No  air  riser  should  be 
less  than  y2  inch,  and  where  the  air  riser  extends 
above  the  second  floor  or  is  connected  to  more  than 
two  air  valves  should  not  be  less  than  £4  inch.  The 
horizontal  air  main  should  be  run  on  the  basement 
ceiling,  and  need  not  be  larger  than  I  inch  except 
in  cases  of  extreme  length,  where  it  should  be  1*4 
inches. 

In  making  up  the  air  lines,  it  is  recommended 
that  galvanized  fittings  be  used  and  that  the  joints 
on  the  air  lines  be  made  up  of  asphaltum  and 
the  fittings  painted  all  over  on  the  outside  with 
asphaltum  in  order  to  close  up  any  sandholes.  Care 
must  be  taken  to  have  the  air  piping  tight.  Care 
must  also  be  taken  to  give  the  air  piping  a  good 
pitch  of  not  less  than  i  inch  to  10  feet  toward  the 
boiler.  The  air  piping  must  contain  no  pockets  or 
traps  of  any  kind.  The  connections  of  the  air  pip- 
ing to  the  air  valves  should  be  made  with  ground 
joint  brass  unions. 

THE    K-M-C    VACUUM    SYSTEM. (MORGAN    PATENTS.) 

In  this  system  the  air  is  forced  out  of  the  radiator  by  raising; 
the  steam  pressure  in  the  boiler,  and  is  prevented  from  re-entering 
the  radiators  by  means  of  the  mercury  seal  in  which  the  end  of 
the  air  line  is  immersed.  Fig.  48  illustrates  an  ordinary  one-pipe 
job  equipped  with  this  system.  At  point  marked  O  on  each  radi- 
ator is  placed  a  retarder,  so-called,  consisting  of  a  bent  tube  of 


Fig.  47. — Mereurv 
Seal. 


Vacuum  and  Vapor  Systems  of  Steam  Heating.        135 

very  small  bore,  designed  to  permit  the  escape  of  air,  but  to  re- 
tard the  escape  of  steam  to  the  air  lines. 

All  the  lines  leading  from  the  retarders  O  are  joined  and  lead 


Fig.  48. — Application  of  Morgan  System  to  One-Pipe  Steam  Radiation. 

to  the  loop  M,  which  should  be  extended  up  a  distance  not  less 
than  15  feet.  The  water  will  back  up  this  loop  about  2.3  feet 
to  every  pound  pressure  carried  on  the  boiler.  At  the  foot  of  the 
loop  a  return  is  run  to  the  boiler  with  a  swing  check  valve  in  the 
return  connection.  The  function  of  the  loop  is  to  condense  the 
steam  mixed  with  air  in  the  vacuum  lines  connected  with  the 


136  Principles    of   Pleating. 

retarders.  The  water  condensed  from  this  steam  backs  up  the 
loop  until  a  hight  is  reached  that  will  overcome  the  pressure 
against  the  check  valve,  when  the  latter  will  be  lifted  and  the 
water  will  return  to  the  boiler. 

From  the  top  of  the  loop  the  main  air  line  leads  to  the  center 
of  the  mercury  seal  illustrated  in  Fig.  47.  The  lower  end  of  this 
center  tube  is  submerged  in  mercury  to  the  depth  of  l/>  inch. 
After  passing  through  the  mercury  at  the  base  of  the  column  the 
air  is  expelled  from  the  system.  By  reference  to  the  cut  it  will  be 
noted  that  the  base  which  contains  the  mercury  is  of  greater 
diameter  than  the  upper  part  of  column.  The  purpose  of  this  is 
to  hold  a  quantity  of  mercury  in  a  thin  sheet,  which  offers  little, 
if  any,  resistance  to  expelling  the  air.  As  the  air  will  not  pass 


Fig.  40. — The  K-M-C  Manual  Retarder. 

down  through  a  liquid  more  dense  than  itself  it  is  impossible  for 
the  air  to  return  to  the  system. 

The  above  description  applies  to  small  plants.  The  system 
may  be  applied  to  two-pipe  installations,  as  set  forth  in  pamphlets 
published  by  the  manufacturers. 

In  the  case  of  larger  plants  "  manual  retarders,"  so  called 
(See  Fig.  49),  are  used  in  place  of  these,  with  a  fixed  opening. 
In  operation  the  manual  retarder  is  designed  to  allow  a  free  flow 
of  air  from  the  pipes  and  radiators  to  the  air  escape  line,  but  to 
offer  a  resistance  to  the  passage  of  steam  and  water.  The  name 
manual  is  given  from  the  fact  that  it  is  operated  by  hand  and 
the  name  retarder  from  the  fact  that  it  prevents  the  escape  of 
steam.  It  has  no  stuffing  box  or  packing,  and  its  operation  in- 
volves the  movement  of  a  disk  of  Helmut  metal.  A  slow  move- 
ment of  the  wheel  opens  and  closes  the  retarder.  The  construc- 
tion provides  for  self  cleaning,  so  that  no  accumulation  may  inter- 


Vacuum  and  Vapor  Systems  of  Steam  Heating.        137 

fere  with  its  operation.  It  may  be  used  on  radiators  which  are 
provided  with  valves,  and  by  closing  both  the  retarder  and  the 
valve  to  the  radiator  complete  isolation  from  the  rest  of  the  system 
is  effected.  Packless  valves  are  recommended. 

An  accumulating  tank  forming  a  storage  chamber  in  the  re- 
turn from  the  air  main  is  provided  as  well  as  other  fixtures  not 
common  to  the  "  loop  system." 

Special  stress  is  laid  on  the  necessity  of  having  a  tight  job 
of  piping.  All  superfluous  boiler  fittings  are  discarded. 

THE  TRANE  VACUUM   SYSTEM. 

In  the  Trane  vacuum  system  air  valves  of  the  expansible  plug 
type  illustrated  in  Fig.  50  are  attached  to  the  radiators,  and  air 
lines  are  joined  and  led  to  the  mercury  seal  shown  at  A  in  Fig.  51, 
which  shows  a  typical  lay  out  of  a  one-pipe  system.  This  method 
of  piping  is  considered  preferable,  not  only  because  of  the  greater 
convenience  of  having  but  one  valve  on  each  radiator,  but  because 
the  fewer  the  valves  the  less  the  leakage  through  stuffing  boxes, 
causing  the  loss  of  vacuum. 

With  this  system  special  care  must  be  exercised  in  packing 
radiator  valves  to  prevent  air  leaking  into  the  system  and  destroy- 
ing the  vacuum.  It  is  claimed,  however,  that  since  the  valves  are 
used  much  less  frequently  than  with  low  pressure  systems,  as 
the  temperature  of  the  house  is  approximately  controlled  by  vary- 
ing the  vacuum  on  the  system,  the  stuffing  boxes  receive  less 
wear,  and  if  well  packed  give  little  trouble  from  leakage. 

This  system  is  so  arranged  that  with  a  steam  pressure  of  a 
pound  or  two,  the  air  in  the  radiators  will  be  forced  through  the 
mercury  and  out  of  the  system.  The  air  valves  prevent  the  escape 
of  steam  from  the  radiators.  When  the  steam  pressure  is  allowed 
to  fall  air  is  prevented  from  entering  the  system  by  the  mercury 
column  which  rises  in  the  pipe.  The  vacuum  has  no  effect  on  the 
water  line  in  the  boiler,  as  the  pressure  on  supply  and  return  lines 
is  the  same.  Of  course,  it  will  be  necessary  from  time  to  time, 
even  in  mild  weather,  to  get  up  sufficient  pressure  to  expel  the 
air  from  the  system,  as  no  job  of  piping  can  be  made  perfectly 
tight.  Every  precaution  must  be  taken,  however,  to  make  the 
system  as  tight  as  possible,  and  all  lines  should  be  thoroughly 


138  Principle    of    Heating. 

tested  with  at  least  30  pounds  pressure,  which  should  be  carried 
for  24  hours  without  serious  loss. 

The  patentees  of  this  system  recommend  that  gauge  cocks  be 
omitted  from  the  water  column,  as  they  are  sometimes  the  source 
of  air  leakage  when  the  system  is  running  under  vacuum.  The 
gauge  glasses  should  be  thoroughly  packed ;  the  stuffing  boxes  on 


Fig.  50. — Trane  System  Air  Valve. 

radiator  valves  must  be  tightly  packed.  The  same  care  must  be 
taken  to  prevent  pockets  in  the  piping  as  with  a  regular  low 
pressure  system.  The  patentees  recommend  that  the  air  pipe  and 
fittings  be  made  of  galvanized  iron  to  avoid  trouble  from  stoppage 
by  scale,  etc. 

Damper  regulators  of  special  design  are  used  in  connection 
with  mercury  seal  systems,  or  thermostatic  control  may  be  ap- 
plied, operating  the  boiler  drafts  from  the  thermostat  located  at  a 


Vacuum  and   Vapor  Systems  of  Steam  Heating.        139 

point  that  will  represent  as  nearly  as  possible  the  average  tem- 
perature of  the  house. 


Fig.   51. — Trane   One-Pipe   Vacuum   System. 
ADVANTAGES    CLAIMED   FOR   THE    MERCURY   SEAL   VACUUM    SYSTEM. 

The  principal  advantages  claimed  for  this  system  of  steam 
heating  over  ordinary  ones  are : 


Principles    of   Heating. 

1.  That  it  is  as  well  adapted  to  mild  weather  as  cold,  whereas 
with  a  steam  heating  system  a  temperature  of  212  degrees  must 
be  attained  to  secure  any  effect  from  the  radiators. 

2.  That  considerable  saving  in  fuel  may  be  effected  in  mild 
weather,  due  to  the  circulation  of  steam  below  atmospheric  pres- 
sure, thus  avoiding  overheating,  so  common  with  low  pressure 
steam  heating.     In  many  sections  in  the  northern  part  of  this 
country  the  average  outside  temperature  during  the  heating  sea- 
son is  35  to  40  degrees  above  zero. 

Steam  heating  systems  based  on  70  degrees  in  zero  weather 
are  difficult  to  control  with  an  .outside  temperature  of,  say,  40 
degrees,  when  the  loss  of  heat  from  a  building  is  only  about  three- 
sevenths  that  in  zero  weather.  The  difference  in  temperature 
between  the  steam  or  vapor  and  the  air  in  the  room  need  be,  under 
the  stated  conditions,  only  three-sevenths  as  much  as  in  zero 
weather. 

3.  The  mercury  seal  vacuum  system  when  applied  to  a  steam 
heating  apparatus   secures  a  \vide   range  in  the  temperature  at 
which  the  radiators  may  be  kept  to  provide  for  different  weather 
conditions. 

The  lack  of  this  range  of  temperature  in  the  ordinary  low 
pressure  steam  system  is  the  greatest  drawback  to  its  successful 
use  in  house  heating.  It  is  said  to  be  practicable  to  maintain  tem- 
peratures varying  all  the  way  from  140  to  230  degrees  or  more, 
which  would  permit  the  system  to  meet  practically  any  outside 
weather  conditions. 

The  following  table  shows  the  temperatures  corresponding  to 
different  pressures : 

TABLE  XXXVIII. 

SHOWING    STEAM     PRESSURE    AND    VACUUM    AND    CORRESPONDING    TEMPERATURE. 

In.  of  mercury.                         Temperature.     Gauge  pressure.  Temperature. 

Vacuum  gauge.                                  Fahr.  Lb.  per  sq.  in.                             Fahr. 

28 101.4  0.304 213.0 

26 125.6  1.3 216.3 

24 .' 147.9  2.3 219.4 

22 152.3  3.3 222.4 

20 161.5  4.3 225.2 

18 169.4  5.3 227.9 

16 176.0  6.3 230.5 

14 182.1  7.3 233.0 

12 187.5  8.3 235.4 

10 192.4  9.3 237.8 

5 203.1  10.3 240.0 

0 212.1 


Vacuum  and  Vapor  Systems  of  Steam  Heating.        141 

The  pressures  are  not  given  in  even  pounds.  The  1.3  pound 
gauge  pressure  corresponds  to  15  pounds  absolute  pressure,  and 
so  on. 

COMPARISON   WITH   HOT   WATER   HEATING. 

Advantages  claimed  for  this  system  over  hot  water  heating 
are: 

1.  Saving  in  cost  of  installation,  as  the  pipes  may  be  made 
smaller  and  smaller  radiators  may  be  used,  owing  to  the  higher 
temperatures  carried  in  cold  weather. 

2.  The  ability  to  increase  or  decrease  the  temperature  in  the 
radiators  more  quickly,  owing  to  the  much  smaller  volume  of 
water  in  the  system. 

3.  The  absence  of  danger  of  drainage  from  leaks. 

On  the  other  hand,  in  weather,  say,  from  50  to  60  degrees, 
when  it  is  only  necessary  to  take  the  chill  off  a  house,  a  hot  water 
system  is  especially  well  adapted  to  fulfill  the  requirements,  and 
the  temperature  of  the  water  may  be  kept  as  low  as  desired, 
whereas  with  the  mercury  seal  vacuum  system  140  degrees  F.  is 
about  as  low  a  temperature  as  can  be  maintained,  and  then  not 
for  any  length  of  time,  owing  to  imperceptible  air  leaks,  which 
destroy  the  vacuum. 

The  advantage  of  quick  heating  in  the  vacuum  system  is,  in  a 
measure,  offset  by  the  advantage  possessed  by  hot  water  for  stor- 
ing the  heat  during  the  night,  insuring  a  warm  house  in  the  morn- 
ing. With  the  mercury  seal  system  all  radiators  are  kept  at  the 
same  temperature.  The  steam  supply  may  not  be  throttled  with- 
out fear  of  water  backing  up  in  the  radiators  and  causing  noise. 
In  hot  water  heating  systems  the  temperature  of  each  radiator 
may  be  controlled  at  will  by  throttling  down  the  supply,  thus 
giving  individual  control  of  the  temperature  of  each  room. 

VACUUM    AIR  VALVES  AND  THE    NORWALL   SYSTEM. 

Several  patterns  of  vacuum  air  valves  have  been  put  on  the 
market  designed  to  permit  the  escape  of  air  from  radiators  and 
to  prevent  its  reentering  them  when  the  steam  pressure  falls. 
With  a  system  perfectly  tight  at  all  valves,  fittings,  etc.,  and  with 
all  vacuum  air  valves  in  working  order  a  steam  plant  may  be  run 
as  a  vacuum  system.  It  can  derive  the  advantage  of  a  great  range 
in  the  temperature  of  the  radiators  by  simply  raising  the  steam 


142 


Principles    of   Pleating. 


pressure  sufficiently  to  drive  out  all  the  air,  for  then  when  the 
pressure  falls  below  that  of  the  atmosphere  the  radiators  will  re- 
main filled  with  steam  at  a  minus  pressure  and  at  a  temperature 
below  the  boiling  point,  viz.,  212  degrees  F. 

Mr.  George  D.  Hoffman  writes  of  the  Norwall  system  as 
follows : 

"  The  difficulty  heretofore  existing  of  being  able  positively  and 


Pig.  52. — The  Norwall  Vacuum  Air  Valve. 

automatically  to  prevent  the  air  from  going  back  into  the  system 
when  the  steam  pressure  is  reduced  below  that  of  atmosphere,  is 
overcome  by  the  use  of  the  Norwall  automatic  air  and  vacuum 
valve  (See  Fig.  52)  and  the  Norwall  air  line  system  of  vacuum 
heating. 


Vacuum  and   Vapor  Systems  of  Steam  Heating.        143 

"  The  valve  is  intended  to  be  a  vacuum  system  in  itself.  With 
an  apparatus  that  is  practically  air-tight  in  all  its  joints  and  con- 
nections, simply  screw  on  the  valves  in  place  of  the  ordinary  air 
valves  and  you  have  installed  a  complete  system  of  vacuum  steam 
heating.  The  use  of  the  Norwall  valve  does  not  necessitate  air 
lines  or  any  mechanical  appliance  for  exhausting  the  air.  Pressure 
exhausts  the  air  from  the  system  through  the  valve,  and  then 
when  pressure  goes  off  the  valve  automatically  closes,  preventing 
the  ingress  of  air  into  the  apparatus  through  the  valve.  The  valve 
is  especially  designed  for  use  in  connection  with  residence  work, 
stores  and  small  apartments  where  the  number  of  radiators  in 
connection  with  any  one  plant  is  limited. 

"  The  Norwall  air  line  system  of  vacuum  steam  heating  is  espe- 
cially designed  for  use  on  large  buildings  such  as  apartment 
buildings,  schools,  hospitals,  asylums,  business  blocks,  etc.  In 
this  system  no  automatic  air  valves  are  used  on  the  radiators. 
Each  radiator  is  fitted  with  a  relief  valve  which  is  open  at  all 
times,  and  which  is  connected  by  a  small  pipe  designated  as  an 
air  line  to  a  vacuum  tank  located  in  the  basement  adjacent  to  the 
boiler.  All  air  from  the  entire  system  is  vented  by  pressure  into 
this  tank  and  from  the  tank  through  a  large  air  valve  either  into 
the  basement,  or  it  can  be  piped  to  a  flue  and  thus  vented  directly 
to  the  atmosphere.  The  advantage  with  the  air  line  system  of 
vacuum  steam  heating  in  a  building  occupied  by  tenants  is  the 
fact  that  the  apparatus  is  at  all  times  in  direct  control  of  the 
engineer  or  fireman."  It  is  not  wise  to  attempt  to  provide  a 
vacuum  system  in  large  buildings  by  simply  attaching  vacuum 
air  valves  to  the  radiators,  because  of  the  great  number  of  valve 
stuffing  boxes,  fittings,  etc.,  at  which  an  inleakage  of  air  is  liable 
to  occur  and  destroy  the  vacuum,  necessitating  the  raising  of 
steam  pressure  at  frequent  intervals  to  force  the  air  out  of  the 
system. 

GORTON   VAPOR  VACUUM    SYSTEM    OF    HEATING. 

In  the  Gorton  Vapor  Vacuum  System  of  Heating,  by  the  use 
of  an  automatic  drainage  valve,  which  is  placed  on  the  return  end 
of  each  radiator,  and  an  automatic  relief  valve,  which  is  connected 
to  the  steam  and  return  mains  in  the  cellar,  it  is  claimed  that 
steam  can  be  circulated  under  a  vacuum,  and  that  the  heat  in  anv 


144  Principles    of   Heating. 

radiator  can  be  controlled  by  graduating  the  opening  of  the  radia- 
tor valve. 

In  this  system  the  hot-water  type  of  radiator  is  usually  em- 
ployed, with  the  steam  inlet  at  the  top  and  the  return  outlet  at 


Fig.  53. — Gorton  Vapor  Vacuum  System  Connections. 

the  bottom.  The  system  of  piping  is  the  ordinary  two-pipe, 
gravity  dry  return,  with  a  loop  seal  at  the  end  of  each  steam  main. 
The  automatic  drainage  valve  is  specially  constructed,  with  a 
brass  cylinder  in  the  body  of  the  valve,  with  a  small  opening  in 
the  side  of  the  cylinder,  which  forms  the  valve  seat.  A  cone- 
shaped  piece  of  metal  projects  from  the  disk  of  the  valve  into  the 
opening  of  the  seat,  which  is  made  at  such  an  angle  as  to  prevent 


Vacuum  and  Vapor  Systems  of  Steam  Heating.        145 

wedging  or  sticking.  The  disk  of  the  valve  is  suspended  from  the 
top  of  the  cylinder,  so  that  it  can  swing  freely  backward  and  for- 
ward, thus  opening  and  closing  the  valve. 

Normally  the  valve  is  closed,  but  a  counterweight  is  applied  in 
such  a  manner  as  to  render  the  opening  of  the  valve  very  gradual, 
according  to  the  difference  in  pressure.  Therefore,  when  a  radia- 
tor valve  is  opened,  the  pressure  of  the  steam  in  the  radiator  will 
force  the  cone  backward,  thus  opening  the  valve  and  allowing  the 
air  in  the  radiator,  and  the  water  of  condensation,  to  pass  through, 
and  down  into  the  return  main,  where  the  air  is  removed  through 


Pig.  54. — Gorton  Vapor  Vacuum  System  Valve. 

the  automatic  relief  valve,  and  the  water  returns  to  the  boiler. 

The  automatic  relief  valve  is  made  in  two  parts.  The  upper 
part,  or  air  valve,  is  connected  to  the  return  main,  and  the  lower 
part,  or  bowl,  is  connected  to  the  steam  main.  In  the  bowl  is  a 
very  sensitive  flexible  diaphragm,  which  is  connected  to  the  valve 
rod.  The  lower  end  of  the  rod  is  connected  with  a  balance  lever 
and  weight,  and  the  upper  end  of  the  rod  terminates  in  the  Jen- 
kins disk  valve  seat  of  the  air  valve.  The  weight  of  the  balance 
lever  is  so  adjusted  that  the  air  valve  will  open  when  the  pressure 
in  the  return  main  equals  that  in  the  steam  main. 

The  system  can  be  run  as  a  vacuum  system  by  simply  raising 
enough  pressure  of  steam  to  expel  the  air  from  all  of  the  radiators, 


146  Principles    of   Heating. 

and  then  allowing  the  fire  to  cool  until  the  desired  amount  of 
vacuum  is  obtained,  after  which  a  low  fire  should  be  maintained. 

BROOMELL'S  VAPOR  SYSTEM  OF  HEATING. 

The  vapor  system  is  a  modified  two-pipe  system  of  steam 
heating,  arranged  with  devices  to  prevent  more  than  a  few  ounces 
pressure  accumulating  in  the  boiler  or  radiators.  Each  radiator  is 
equipped  with  a  special  supply  valve  shown  in  Fig.  56,  designed 


Fig.  55. — Gorton  Vapor  Vacuum  System  Differential  Controller. 

to  admit  a  volume  of  vapor  or  low  pressure  steam  sufficient  to 
supply  a  portion  or  all  of  the  radiating  surface.  At  the  return 
end  of  each  radiator  is  placed  a  small  combined  water  seal  and 
air  vent  (see  Fig.  57),  designed  to  permit  the  escape  of  air  and 
the  water  condensed  in  the  radiator.  Fig.  58  shows  a  radiator 
equipped  with  the  supply  valve  and  the  combined  water  seal  and 
air  vent.  Radiators  of  the  hot  water  type  are  invariably  used  in 
connection  with  this  system. 

The  returns  from  the  radiators,  this  being  a  two-pipe  system, 


Vacuum  and  Vapor  Systems  of  Steam  Heating.        147 

are  combined  in  the  basement  and  lead  to  a  receiver  (see  Fig.  59) 
connected  with  the  boiler.  The  main  return  is  sealed  at  the  end,  as 
illustrated  in  Fig.  60,  to  prevent  the  escape  of  vapor  to  the  cellar. 
From  the  chamber  C  the  air  combined  with  some  vapor  from 


Fig.  56. — Vapor  System  Supply  Valve. 


Pig.  57. — Union  Elbow  for  Return  End  of  Radiator. 

the  system  escapes  through  the  air  line  to  the  condensing  radi- 
ators suspended  from  the  basement  ceiling  as  shown  in  Fig.  59. 
The  vapor  is  condensed  in  these  radiators  and  flows  back  by  grav- 
ity to  the  boiler,  the  air  escaping  to  the  smoke  flue.  The  latter  is 
preferable  to  any  other  point  of  escape  since  the  heat  in  the  flue 
causes  a  slight  pull  on  the  air  line  accelerating  the  removal  of 
the  air  from  the  system. 


Principles    of   Heating. 


The  receiver  is  open  at  the  top,  and  there  is  no  check  valve 
between  it  and  the  boiler.  It,  therefore,  acts  as  a  perfect  safety 
valve  to  prevent  any  excess  of  pressure  in  the  boiler.  Should 
the  boiler  pressure  increase,  the  water  would  be  driven  out  into 
the  receiver.  The  float  therein  would  be  raised  and  the  drafts 
closed.  Should  the  pressure  continue  to  increase  from  any  cause 


Fig.  58. — Radiator  Connected  on  Vapor  System. 

the  float  in  the  receiver  would  rise  until  the  lever  of  the  relief 
valve  is  raised,  permitting  the  escape  of  steam  and  reducing 
the  pressure.  A  glass  water  gauge  is  attached  to  the  receiver,  and 
a  scale  indicates  the  boiler  pressure  in  ounces.  No  other  pressure 
gauge  is  necessary. 

The  maximum  pressure  never  exceeds  13  ounces,  and  therefore 
the  size  of  the  radiators  must  be  based  on  relatively  low  tempera- 
tures, and  an  amount  of  surface  within  10  or  15  per  cent,  of  that 


Vacuum  and   Vapor  Systems  of  Steam  Heating.        149 

required  with  hot  water  heating  is  commonly  provided  to  warm 
the  rooms  properly  in  the  coldest  weather.  With  this  system  one 
cannot  overcome  the  effect  of  a  shortage  in  radiating  surface  by 
increasing  the  pressure  and  temperature  as  in  low  pressure  steam 


/CONDENSING  RADIATOR 


AIR  VENT  TO  CHIMNEY    _ 


RFCE.IVER.  OPE.N  AT  TOP 


PIPE  TO  STEAM  SPACE 
IN.  BOILER 


•COPPER  FLOAT 
CONNECTED  BY  CHAIN 
WITH  DAMPERS 


JrfAlN  RETURN;  TO  JBOILEB 


Fig.  59. — Connections  at  Boiler,  Showing  Condensing  Coil. 

heating,  since  the  water  would  be  backed  out  of  the  boiler  through 
the  main  return  connected  with  the  receiver. 

The  water  line  of  the  boiler  should  be  at  least  4  feet  below 
the  basement  ceiling  to  give  sufficient  pitch  to  the  pipes  and  to 
provide  ample'  hight  to  cause  the  water  to  flow  back  into  the 
boiler.  A  common  arrangement  of  piping  is  shown  in  Fig.  61. 


1 50  Principles    of    Heating. 

The  returns  must  be  run  overhead  in  the  basement,  that  is,  they 
must  be  "  dry."  These  pipes  are  preferably  left  uncovered  in 
order  to  promote  the  condensation  of  any  vapor  escaping  to 
them  from  the  radiators. 

The  vapor  system  may  be  used  in  connection  with  exhaust 
steam  plants  supplemented  by  live  steam  and  with  central  heating 
plants,  as  shown  in  Fig.  62.  When  the  condensation  is  not  re- 
turned to  the  boilers  the  pump  and  receiver  are  omitted,  and  the 
condensation  is  discharged  to  the  sewer  through  a  cooling  coil. 
Central  station  heating  companies  commonly  require  the  cooling 


OPEN  AT  TOP 


SECTION 
THROUGH  RECEIVER 


Fig.  60.— Seal  at  End  of  Main  Return. 

coil  on  low  pressure  systems  to  contain  one-fifth  to  one-sixth  of 
the  entire  direct  radiating  surface  in  the  building. 

ADVANTAGES   CLAIMED  FOR  THE  VAPOR  SYSTEM. 

1.  The  control  of  the  heat  given  off  by  each  radiator  inde- 
pendently by  means  of  the  quintuple  valve  shown  in  Fig.  56,  which 
may  be  set  to  admit  any  desired  amount  of  steam.   This  is  of  great 
value  when  there  is  but  one  radiator  in  a  room,  for  with  ordinary 
steam  heating  one  has  practically  no  control  of  the  room  tempera- 
ture under  these  conditions. 

2.  Freedom  from  any  danger  of  over-pressure  on  the  boiler. 
The  safety  valve  of  an  ordinary  system  may  stick  or  the  water 
in  the  expansion  pipe  of  a  hot  water  system  may  become  frozen. 

3.  Economy  in  fuel  because  of  the  easy  control  of  temperature 
afforded,  thus  avoiding  overheating. 

4.  Much  smaller  pipes  may  be  used  than  with  low  pressure 


Vacuum  ana f-  Vapor  Systems  of  Steam  Heating. 


152 


Principles   oj    ii  eating. 


Vacuum  and  Vapor  Systems  of  Steam  Heating.         153 

steam  or  hot  water  heating.  With  the  vapor  system  the  supply 
connections  practically  never  exceed  ^J  inch  in  size,  and  the  re- 
turns y2  inch  for  direct  radiators. 

5.  Air  valves  are  not  required,  the  air  being  removed  through 
the  small  vent  in  the  special  fitting  attached  to  the  return  end  of 
each  radiator. 

6.  Quick  heating  ability.     A  vapor  may  be  very  quickly  se- 
cured sufficient  to  fill  the  radiators  without  forcing  the  fire. 


INDEX. 


Air,  Weight  of,  per  cubic  foot 3* 

"     Capacity  of,  to  absorb  moisture 34 

"     Heat  brought  in   by 43 

"     Temperature  of,  at  inlet 45 

"     Specific  heat  of 46 

Aspirating  coils 48 

Babcock's  formula  fcr  flow  of  steam  in  pipes 81 

Back  pressure,  Effect  of 105 

Counteracting  by  increased  boiler  pressure 106 

Blower  coils.  Heat  given  off  by 44 

"       See  Heaters. 

"       How  compute  size  of .-. , .; 45 

"       Size   of   required .  ./.>... ... ...  .65-66 

Boiler  connections,    Sizes   of iiv.  . . . . ., .   103 

Boilers,  Efficiency  of 8-9 

Proportion  of  heating  to  grate  surface .......11-23 

Horse  power  required  to  heat  given  space. .63-66 

Capacities   of ,23 

How  compute  size  of 23 

Boiler  Horse  Power,  expressed  in  heat  units -S 

"       ratings 24' 

Briggs'  formula  for  steam  pipes 95 

British  Thermal  Unit   (B.  T.  U.),  or  Heat  Unit,  Definition  of 7 

Broomell  System,  Description  of .14610  153 

Charts  for  computing  steam  radiating  surface  required :. .  .'57-59 

Hot    water 61-62 

Child,  E.  T.,  Article  by,  on  Steam  Mains 94  to  - 

Coal,  Heating  power  of , . .      8 

Coke,        "  "         "     ..       8 

Coils,  Heat  given  off  by 37,  39,  40 

"      Aspirating  48 

for  heating  water,  Efficiency  of 68-69 

Combination  heaters,  Tests  on .     IT 

Types  of 11-12-13-14-15 

Capacity  of 16 

Combustion,  Rate  of  in  boilers 10,  23,  24 

Condensation  of  steam,  Effect  of,  in  pipes 85 

D'Arcy's  formula  for  flow  of  steam  in  pipes 81 

Donnelly  system,  Description  of 127-128 

Efficiency  of  boilers 9 

Evaporation,   Heat   required   for ! 9 

"  "      required   to   effect  same 34 


156  Principles    of   Heating. 

K-M-C-  System,  Description  of 134  to  137 

Liquids,  Boiling  of,  in  vats 70 

Mains,  Hot  water,  Capacities  of,  for  direct  heating iio-in 

For  direct  heating,  various  authorities iu 

"     indirect  heating   112-113 

Sizes  of,  for  low  pressure  steam  heating 88-99-100 

Steam,  Velocities  in 100-101 

"       Circuit,  Capacity  of 102 

Returns,   Sizes  of   92 

'    for  two  pipe  vacuum  systems 93 

"       Sizes  of,  for  steam  heating 88-89 

"     "      "   vacuum  system   92-93 

Chart  and  table  showing  capacities  of,  according  to  different 

rules  97-98 

M'Gonagle  System,  Description  of 131  to  134 

Mechanical  equivalent  of  heat 33 

Morgan  System,  Description  of 134  to  137 

Norwall  System  and  air  valves — Description  of 141  to  143 

Paul  System,  Description  of 123  to  126 

Persons,  Heat  given  off  by 8 

Petroleum,  Heating  power  of 8 

Pipes,  Capacities  of,  for  hot  water  heating no-ill 

"      Resistance  in,  to  flow  of  water no 

Pipes.    See  Risers. 
Pipe  sizes: 

Briggs'  formula 95 

Tudor's       "        95 

Baldwin's  rule 95 

Wolff's         " ...95-96 

Pipes,  see  Mains. 

"      Capacities  of,  expressed  in  amount  of  radiation  supplied 88 

"      Exhaust  for  Engines 104 

"      Steam  *'  104 

"      Flow  of  steam  in 81-82 

"       "       "        "    Example,  illustrating  use  of  tables 85 

"          "       "       "        "    wi-h  more  than  40%  drop  in  pressure 86 

"     Heat  given  off  by. 40 

"      Relative  capacities  of 86 

"      Equation  of  (Table) 87 

Radiation,   see  Radiators. 

Indirect  steam,  How  compute  amount  required 41 

Indirect;    Temperature   at   Inlet 45 

Relation  between  direct  and  indirect 43 

How  compute  on  a  heat  unit  basis 54-55-56 

"  Hot  Water,  How  Compute  by  Charts 61  to  63 

"  Direct  steam,  How  compute  by  charts 57  to  60 


Index.  157 

Electrical  heat  units 8 

Electric  heaters   18-19-20 

"        heating,  Cost  of 21 ' 

Combined  efficiency  of  apparatus  required 22 

Elbows  and  bends 84 

Resistance    of    '. 96-115 

Electricity,  Heating  power  of 8 

Engines,  Steam  and  exhaust  pipe  sizes 103-104 

Condensing,  Steam  heating  in  connection  with 106 

Expansion  tanks.  Capacity  of 1 16 

Factors  for  use  in  computing  pipe  sizes 83-84 

Feed  water  heaters,  Proportion  of 68 

Flue  area,  Relation  between  flue  area  and  indirect  surface 42-43 

Flues,  Velocities  in 28,  50 

Fuels,  Heating  power  of 8 

Fuel,  Amount  of  per  season 25 

Furnaces,  Proportions  of  heating  to  grate  surface n 

Rate  of  combustion   in 27 

Tests  of  '. , 27-28-29-30 

Furnace  Heating,   Temperature  of  air  supply 28 

Velocity  of  air  in  pipes 28-29-30 

Gas,  Heating  power  of 8-17 

heaters    79 

Glass    Surface,    Equivalent 45 

Loss  of  heat  through 56 

Gorton    System,    Description   of 143  to  146 

Heat,  Loss  of,  from  rooms 21 

"  by  transmission  through  walls,  glass,  etc 53-54 

How  compute  loss  of 54-55 

Relative  loss  of,  from  buildings  of  different  forms 65-67 

unit,  Definition  of 7 

Heaters  combined   with   fans 44-45,   66-67-99 

Supplementary    44-45 

Aspirating 48 

Heating  Surface,  Ratio  of,  to  grate 10-11 

Horse  power  of  boiler  in  heat  units 8 

Hot  Water  Heating 108  to  116 

See  Water. 

Hot  water  combination  heaters,  Tests  on II 

Types  of  11-12-13-14-15 

Capacity    of , 16 

generators     69-70 

Heaters   for   water  supply 75-76-77-80 

Humidity    34~35 

Ice,  Heat  units  absorbed  in  melting 32 


158  Principles    of   Heating. 

Kerosene,  Heating  power  of 8 

for   heating    , 17-18 

Radiator  Connections,  Sizes  of,  for  Hot  Water 113 

Radiators,  Hot  water,  Indirect,   Pipe  sizes  for 112-113 

Direct  steam,  Heat  given  off  by 36-37-38-39-40,  94 

Indirect  steam,  Heat  given  off  by 41 

"  when  used  with  fans ...     99 
Direct,  Heat  given  off  by,  in  rooms  at  different  temperatures    40 

Refrigeration 33 

Returns,  Steam  heating,  Sizes  of 92 

Risers,   Steam,  Velocities  in 91-102 

Hot  water,  Capacities  of 1 13-114 

"       Steam,  Capacities  of 89-90 

One  pipe  91 

Two  pipe   92 

Specific  heat 31 

of  air  31-46 

Steam  Heating  in  connection  with  Condensing  Engines 106-107 

"      pressure   and  vacuum  and  corresponding  temperature,    Table 

showing 140 

Steam,  flow  of  in  pipes 81  to  86 

'    with  more  than  40%  drop  in  pressure 86 

Swimming  pools,  Heating  of 71-72-73-74-75 

How  compute  boiler  capacity  required 73-74 

"      How  compute  heating  surface  required 74 

Tables.     See  list  of  tables  in  Table  of  Contents. 

Tanks,    Expansion,    capacities    of 116 

Tank  heaters,  Capacity  of 75-76-77 

Efficiency    of    80 

Thermograde  System,  Description  of 128  to  131 

Trane  System,  Description  of 137  to  141 

Tudor    formula  for  steam  pipes 95 

Vacuum  System,  Pipe  sizes 92-93 

Vapor  System,   Description  of 146  to  153 

Ventilation,  Loss  of  heat  by 41-46 

Water,  Flow  of,  in  pipes 108 

Heating  of,  by  steam  pipes 68 

Volume  of,  to  supply  radiators 109 

"       Weight  of  distilled 1 10 

Velocity  of,  in  heating  pipes no 

How  compute  surface  required  for  heating 68 

"       backs,  Proportions  and  capacity  of 77-78-79 

Webster  system,  Pipe  sizes 92-93 

Description  of   1 17  to  122 

Wood,  Heating  power  of 8 


Index.  159 

ILLUSTRATIONS. 


Figure. 

1  ..........  Horizontal  Tubular  Boiler  ......................  ........  8 

2  ........  .  .  Water  Tube  Boiler  ............................  .  .  .......  9 

3  ..........  Sectional  Cast  Iron  Boiler  with  Vertical  Sections  ........  10 

4  ..........  Sectional  Cast  Iron  Boiler  with  Horizontal  Sections  ......  n 

5  ..........  Dome  Water  Heater  ...................................  12 

6  ..........  Ring  Water  Heater  ....................................  12 

7  ..........  Combined  Ring  and  Dome  Heater  ...............  .  ......  13 

8  ..........  Deep  Ring  Water  Heater  ..............  .  ................  13 

9  ..........  Pipe  Coil  Water  Heater  ........................  .......  14 

,    10  ..........  Auxiliary  Heater  for  Combination  Heating.  ^  .  ..........  14 

II.  ..  .......  Types  of  Dome  Heater  for  Combination  Heating  ........  15 

12  ..........  Disk  Heater  for  Combination  Heating  ..................  15 

13....  ......  Overhanging  Type  of  Auxiliary  Heater  ..............  ...  15 

14  ..........  Maltese  Type  of  Auxiliary  Heater  .......................  16 

15  ..........  Type  of  Electric  Radiator  ..............................  18 

I5A  ........  Luminous  Electric  Radiator  ............................  19 

156  ........  Non-Luminous   Electric  Radiator  .......................  20 

16  ..........  Plan,  and  Front  and  Side  Elevations,  Concealed  Radiator.  36 

17  ........  .  .  Indirect  Radiator  Connections  ----  .  ..................  ..  .  .  42 

18  ..........  -Blower  System  Heater  .....  .  ............................  43 

19!  .........  A  Heater  for  Blower  Use  ..............................  44 

20  ..........  Supplementary  Heater  or  Reheater  ......................  45 

21  ..........  Fan  Blowing  Air  Through  Heater  ......................  46 

22  ..........  Fan  or  Blower  Drawing  Air  Through  Heater  ...........  46 

23  ..........  Section  Through  Vent  Flue  Showing  Aspirating  Coil  ----  47 

24  ..........  Elevation  of  Aspirating  Heater  on  Line  A-B  ............  47 

25  ..........  Plan  of  Ducts  Connected  with  an  Aspirating  Heater  ......  49 

26  .........  /Elevation  of  System  on  Line  AB  of  Fig.  25  ..............  51 

26A  ........  Variation    in    Exposure    in     Buildings    of    Equal    Cubic 

Contents     .........................................  65 

27  ..........  Hot  Water  Storage  Tank  Heated  by  Steam  ..............  69 

28  ..........  Arrangement  of  Heater  Connected  with  Swimming  Pool  72 

29  ..........  Tank  Heater  Connections  ..............................  76 

30  ..........  Gas  Heater  Connected  with  Range  Boiler  ...............  78 

31  and  32.  .  .  Methods  of  Dripping  Risers  ............................  90 

33  ..........  Head  of  Water  Causing  Flow  ..........................  108 

34  ..........  Webster  Water  Seal   Motor  ............................  118 

35  ..........  Webster  Water  Seal  Motor  .............................  119 

36  ..........  Typical   Radiator   Connections  ..........................  120 

*    37  ..........  Typical  Arrangement  of  Vacuum  Pump  and  Feed  Water 

Heater  in  Webster  Vacuum  Heating  System  .........  121 

38  ..........  Front  Elevation  of  Paul  Exhausting  Apparatus  ..........  123 

39  ..........  Paul   System  Connections  for  One-Pipe  System  .........  124 

40  ..........  Paul   System  Connections  for  Two-Pipe  System  ........  124 

41  ..........  Differential  Pressure  Controlling  Valve  .................  127 


160  Principles   of   Heating. 

Figure.  Page. 

42 Impulse  Automatic  Valve . .   127 

43 Application  of  the  Donnelly  System  to  Radiating  Coils. . .   128 

44 Thermograde  Control  Valve 129 

45 Radiator  Equipped  with  Thermograde  Valves. 130 

46 Typical  Arrangement  of  the  McGonagle  Vacuum  Heat- 
ing System 132 

47 Mercury  Seal 134 

48 Application  of  Morgan  System  to  One-Pipe  Steam  Radia- 
tion    135 

49 The  K.  M.  C.  Manual  Retarder 136 

50 Trane  System  Air  Valve 138 

51 Trane  One-Pipe  Vacuum  System 139 

52 The  Norwall  Vacuum  Air  Valve 142 

53 Gorton  Vapor  Vacuum  System  Connections    144 

54. Gorton  Vapor  Vacuum  System  Valve   145 

55 Gorton  Vapor  Vacuum  System  Differential   Controller...  146 

56 Vapor  System  Supply  Valve 147 

57 Union  Elbow  for  Return  End  of  Vapor  Radiator 147 

58 Radiator  Connected  on  Vapor  System 148 

59 Connections  at  Boiler  Showing  Condensing  Coil 149 

60 Seal  at  End  of  Main  Return 150 

61 The  Vapor  System,  Showing  Manner  of  Running  Steam 

and  Return  Pipes 151 

62 The  Vapor  System,   Showing  Manner  of  Heating  from 

High  Pressure  Boilers 152 

CHARTS. 

Chart.  Page. 

i Ratios  for  Direct  Steam  Radiating  Surface  to  Rooms  with 

Two  Sides  Exposed  Toward  North  and  West,  with 
Glass  Surface  Aggregating  25  per  cent,  of  Total 
Exposure 57 

2 Ratios  for  Direct  Steam  Radiating  Surface  in  Rooms  Hav- 
ing Only  One  Side  Exposed  Toward  North  or  West, 
with  Glass  Surface  Aggregating  20  per  cent,  of  Total 
Exposure  59 

3 Ratios  for  Direct  Hot  Water  Radiating  Surface  Open 

Tank  System  in  Rooms  with  Two  Sides  Exposed 
Toward  the  North  and  West,  with  Glass  Surface 
Aggregating  20  per  cent,  of  Total  Exposure 61 

4 Ratios  for  Direct  Hot  Water  Heating  Surface,  Open 

Tank  System,  in  Rooms  with  Only  One  Side  Ex- 
posed Toward  the  North  or  West,  with  Glass  Surface 
Aggregating  20  per  cent,  of  Total  Exposure 62 

5 Cubic  Contents,  Showing  Space  Heated  per  Boiler  Horse 

Power  in  Isolated  Buildings  Under  Conditions  Stated  63 


Index.  161 

Chart.  Page. 

6 Cubic  Contents,  Showing  Boiler  Horse  Power  for  Isolated 

Building  Under  Conditions  Stated 66 

6A Size  of  Steam  Main,  According  to  Different  Rules 97 

TABLES. 

Table.  Page. 

I.  Ratings  of  Combination  Heaters 16 

II.  Anemometer  Tests — Furnace  Heating 28 

III.  Flue  Velocities — Furnace  Heating 30 

IV.  Weight  of  Air,  per  Cubic  Foot 32 

V.  Weight  of  Water  Vapor,  per  Cubic  Foot 34 

VI.  Steam  Radiator  Tests 39 

VII.  Loss  of  Heat  From  Pipes 40 

VIII.  Heat  Given  Off  by  Indirect  Radiators 41 

IX.  Flue  Velocities  50 

X.  Loss  of  Heat  Through  Brick  Walls 53 

XL  Loss  of  Heat  Through  Stone  Walls 53 

XII.  Loss  of  Heat  Through  Pine  Planks 53 

XIII.  Loss  of  Heat  Through  Glass,  Etc 54 

XIV.  Loss  of  Heat  Through  Partitions,  Floors,  and  Ceilings...  54 
XV.  Factors  for  Exposure,  Etc 54 

XVI.  Flow  of  Steam  in  Pipes 82 

XVII.  Factors  for  Different  Pressures  82 

XVIII.  Factors  for  Different  Drops  in  Pressure 83 

XIX.  Factors  for  Different  Lengths 83 

XX.  Resistance  at  Entrance  to  Pipes 84 

XXI.  Equation  of  Pipes 87 

XXII.  Capacities  of  Steam  Pipes,  Expressed  in  Direct  Radiating 

Surface  88 

XXIII.  Capacities,  Up- Feed,  One-Pipe  Steam  Risers 91 

XXIV.  Capacities,  Up-Feed,  Two-Pipe  Steam  Risers 92 

XXV.  Capacities  of  Returns  Two-Pipe  Vacuum  Systems 93 

XXVI.  Capacities,  Steam  Mains 98 

XXVII.  Sizes  of  Main  Pipes  for  Boilers 103 

XVIII.  Sizes  of  Supply  Pipes  for  Engine 104 

XXIX.  Sizes  of  Exhaust  Pipes  for  Engine 104 

XXX.  Volume  and  Weight  of  Distilled  Water no 

XXXI.  Capacities  of  Hot  Water  Mains  (by  the  author) in 

XXXII.  Capacities  of  Hot  Water  Mains  (various  authorities) 112 

XXXIII.  Capacities  of  Hot  Water  Pipes  for  Indirect  Radiation...  113 

XXXIV.  Comparison  of  Ratings  for  Hot  Water  Risers 113 

XXXV.  Capacities  of  Hot  Water  Risers  (by  the  author) 114 

XXXVI.  Capacity  of  Expansion  Tanks 116 

XXXVII.  Pipe  Sizes,  Thermograde  System 131 

XXXVIII.  Temperatures  Corresponding  to  Different  Steam  Pressures  140 


OVERDUE. 

N-T26   1932 


LD  2l-50.n-8.-32 


161903 


>7>c>  W 


